CoFe2O4 Composite

Article Cite This: Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Polymorphism and Phase Transitions in t‑ZrO2/CoFe2O4 Composite Structures: Impact of Composition and Heat Treatments Subina Raveendran and S. Kannan* Centre for Nanoscience and Technology, Pondicherry University, Puducherry-605 014, India

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S Supporting Information *

ABSTRACT: A series of Zr4+, Y3+, Fe3+, and Co2+ combinations in solution form and their subsequent potential to yield the desired ZrO2/CoFe2O4 composite that possesses better structural stability at 1300 °C have been presented. The results emphasized the combined effect of heat treatment temperatures and concentration variations in Fe3+/ Co2+ to retain tetragonal ZrO2 (t-ZrO2) and CoFe2O4 structures. The incidence of a gradual m- → t-ZrO2 transition alongside the enhanced phase yield of CoFe2O4 is determined. Despite the invariable presence of 8 mol % of Y2O3 in all the investigated systems, the results revealed the inability to establish t-ZrO2 stabilization at 900 and 1100 °C. XPS analysis confirms the oxidation states of iron, yttrium, cobalt, and zirconium in their respective 3+, 3+, 2+, and 4+ in the ZrO2/CoFe2O4 composite. Morphological analysis revealed the presence of distinct grains pertinent to ZrO2 and CoFe2O4 alongside pore free microstructures. The resultant microstructures demonstrated better hardness and Young’s modulus values, and moreover, the gradual increment in the phase content of CoFe2O4 in the composite revealed a corresponding surge in the ferrimagnetic features.

1. INTRODUCTION The exceptional physical and chemical stability, enhanced hardness, magnetic anisotropy, and electrical resistivity of spinel ferrites gain attraction in a wide range of applications such as magnetic storage devices, sensors, biomedical implants, hyperthermia, and carrier fluids.1−3 The superior magnetic features and low inherent toxicity of ferrites have been derived to serve as medical diagnostic and therapeutic agents.4−6 Cobalt ferrite (CoFe2O4) is an important candidate preferred in magnetic hyperthermia therapy due to the high magneto crystalline anisotropy that emerges from the spin−orbital coupling at the crystal lattice.7,8 The inverse spinel structure of CoFe2O4 comprises divalent and trivalent cations that, respectively, occupy the octahedral B and tetrahedral A sites, while oxygen is positioned at the interstitial sites. This unique structure of CoFe2O4 prefers the accommodation of trivalent and divalent dopants in its lattice devoid of significant structural distortion.9 The self-heating ability of CoFe2O4 has been explored in magnetic hyperthermia therapy (MHT) that demonstrates the preference to destroy only tumor cells, leaving the normal cells unperturbed at an operating temperature of ∼43 °C.10−16 The concept of MHT to treat osteosarcoma gains tremendous attraction during recent years. In this context, the design of a biomaterial with optimum Curie temperature in vivo to destroy tumor cells alongside the role of viable bone substitute with exceptional mechanical stability remains an ardent task.17,18 The superparamagnetic characteristics and bone regeneration capacity of iron doped hydroxyapatite (HAP) has been explained by Tampieri et al.19,20 Iwasaki et al. report the effective heating ability of an Fe3O4/HAP composite.21 The © XXXX American Chemical Society

synthesis and hyperthermia property of HAP-ferrite hybrid particles by ultrasonic spray pyrolysis has also been reported.22 On the contrary, exceptional mechanical stability of ZrO2 receives negligible attraction in osteosarcoma treatment. ZrO2 is usually processed at high temperatures to accomplish the desired mechanical stability.23 The integration of metal ferrites in ZrO2 or in composite form is expected to divulge dual features of appropriate magnetic and mechanical properties essential for osteosarcoma. Nevertheless, the integration of metal ferrites with ZrO2 in composite form is perplexing due to the shortcomings involved in the structural stabilization of metal ferrites at elevated temperatures. Among the bioceramics preferred in hard tissue replacement, ZrO2 enjoys superior advantages of exceptional biocompatibility, mechanical stability, toughness, and the better structural stability displayed at elevated temperatures.24,25 On the other hand, integration of CoFe2O4 in a ZrO2 matrix alongside preserving structural stability at elevated temperatures is an interesting and demanding topic. The structural stabilization of ZrO2 in either tetragonal (t-ZrO2) or cubic (cZrO2) form is achieved with the aid of varied concentrations of Y2O3 stabilizer ranging from 3 to 8 mol %.26−28 Nevertheless, the inclusion of cobalt and iron in the ZrO2 system to establish individual structures of ZrO2 and CoFe2O4 at elevated temperatures has been scarcely documented. In this pursuit, the present investigation aims to attain a structurally stable Received: May 2, 2019 Revised: June 22, 2019

A

DOI: 10.1021/acs.cgd.9b00583 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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2.3. Mechanical Characterization. The selective mechanical properties, namely, hardness and Young’s modulus, of the composite specimens were determined using the nanoindentation technique (Bruker). In a brief description of the procedure, initially, the volatile impurities from powder samples were eliminated through treatment at 700 °C, and subsequently, powders were milled in a planetary ball mill (Retsch, Haan) for a period of 2 h. The resultant powders were pressed into a pellet size of 13 mm in diameter and 1 mm in thickness using a semiautomatic hydraulic press under an applied load of 10 kN for 60 s, followed by 1300 °C heat treatment with a dwell time of 2 h. Thus, the obtained pellets were fine polished using diamond paste to establish surface smoothness. Multiple indents were implemented at random areas to obtain the desired mechanical parameters. Surface morphology of the specimens prior to polishing was attained from a field emission scanning electron microscope (FESEM, Carl ZEISS Microscopy).

ZrO2/CoFe2O4 composite at elevated temperatures. The concentrations of Zr4+, Y3+, Fe3+, and Co2+ in solution form have been varied to obtain the composite structures. The role of temperature, compositional variations, phase transitions, and the chemical interaction among elements has been investigated. This is followed by the evaluation of morphological features, selective mechanical properties, and magnetic features of the ZrO2/CoFe2O4 composite system.

2. EXPERIMENTAL METHODS 2.1. Synthesis. Five different ZrO2/CoFe2O4 combinations were attempted through a citrate assisted sol−gel combustion technique. Analytical grade precursors of zirconium oxychloride [ZrOCl2·8H2O], ferric nitrate [Fe(NO3)3·9H2O], cobalt nitrate [Co(NO3)2·6H2O] and yttrium nitrate [Y(NO3)3·6H2O], and citric acid (C6H8O7) were used for the synthesis process. The concentrations of Co2+/Fe3+ were varied, whereas the content of ZrO2 precursor has been maintained in all the synthesis. 8 mol % Y3+ was invariably used in all the syntheses to establish ZrO2 stabilization, and moreover, 8 mol % Y3+ stabilized ZrO2 (8YSZ) was also synthesized for effective comparison. Table 1

3. RESULTS 3.1. Qualitative Phase Analysis. Figure 1 presents the XRD patterns of five different Co2+/Fe3+ combinations in 8YSZ recorded at three different temperatures. The diffraction patterns at 900 °C (Figure 1a) accomplished the existence of major reflections typical of monoclinic zirconia (m-ZrO2) alongside tetragonal zirconia (t-ZrO2) in all the compositions; however, a close analysis of the results indicated a gradual reduction and simultaneous surge in the reflections respective of m-ZrO2 and t-ZrO2 as a function of enhanced Co2+/Fe3+ additions. Further, a gradual increment in the reflections typical of CoFe2O4 with respect to the enhanced Co2+/Fe3+ additions is obvious in all the compositions. XRD patterns at 1100 °C (Figure 1b) displayed a similar trend with the data obtained at 900 °C; however, a further decline and the simultaneous increment in the reflections respective of m-ZrO2 and t-ZrO2 were apparent at 1100 °C. In the case of the XRD data obtained at 1300 °C (Figure 1c), a contrasting trend has been noticed that demonstrated the stabilization of t-ZrO2 and CoFe2O4 in 40CFZ, 60CFZ, and 100CFZ. 10CFZ and 20CFZ still indicated the trace of m-ZrO2 reflections at 1300 °C. Thus, the simultaneous role of the Co2+/Fe3+ concentration gradient and temperature dependent crystallization of the selective phases was affirmed. It should be noted that the phase behavior of 8YSZ demonstrates the complete stabilization of t-ZrO2 until 1300 °C. With an aim to understand the importance of Y3+ in the system, the synthesis of cationic mixtures comprising only Y3+, Co2+, and Fe3+ devoid of Zr4+ additions was carried out and the resultant phase behavior was analyzed at 900 and 1300 °C (Supporting Information, Figure S1). Two different compositions were designed, one being the concentration of Co2+/Fe3+ mixtures lower than the overall Y3+ and other being the vice versa. In both the cases, XRD results ensure the crystallization of a set of phases, namely, YFeO3, YCoO3, Y2O3, and Co3O4, at both 900 and 1300 °C. In terms of low Co2+/Fe3+ content, the crystallization of YFeO3, YCoO3, and Y2O3 was evident, while the excess Co2+/Fe3+ demonstrated YFeO3, YCoO3, and Co3O4 at 900 and 1300 °C. This result affirms the enhanced propensity of Y3+ to favor individual interaction with Co2+ and Fe3+, and moreover, the crystallization of CoFe2O4 is found negligible in both the systems. In an another experiment, the synthesis was performed with the precursors involving Co2+, Fe3+, and Zr4+ devoid of Y3+ additions, and the resultant phase behavior was analyzed at two different temperatures (Supporting Information, Figure S2). Two different combinations of lower (10 mol % of Co2+ and Fe3+) and higher (100 mol % of Co2+ and Fe3+) concentrations

Table 1. Molar Concentrations of the Precursors Used in the Synthesis sample code

ZrOCl2

Y(NO3)3

Fe(NO3)3

Co(NO3)2

YZ 10CFZ 20CFZ 40CFZ 60CFZ 100CFZ

0.50 0.50 0.50 0.50 0.50 0.50

0.04 0.04 0.04 0.04 0.04 0.04

0.025 0.050 0.100 0.150 0.250

0.025 0.050 0.100 0.150 0.250

illustrates the sample codes and their corresponding details on precursor concentrations utilized for attaining different compositions. In a brief description of the synthesis protocol, the individual stock solutions comprising metallic nitrates of Zr4+, Fe3+, Co2+, and Y3+ were mixed under constant stirring conditions at 90 °C, and subsequently, citric acid was added to the reaction mixtures after 10 min. The resultant mixtures were subjected to continuous stirring until the formation of a viscous gel and thereafter dried overnight at 120 °C. 2.2. Powder Characterization. The synthesized powders were heat-treated at predetermined temperatures in the range of 900, 1100, and 1300 °C for structural and composition analysis. All the heat treatments were performed individually with a heating rate of 5 °C/min to attain the desired temperature, followed by a dwell time of 4 h, and thereafter cooled to room temperature at ambient conditions. X-ray diffractometer (RIGAKU, ULTIMA IV) measurements with Cu Kα radiation (λ = 1.5406 Å) produced at 40 kV and 30 mA were recorded within the scan range of 5° and 90° 2θ with a step size of 0.01° 2θ/s to analyze the phase composition. The crystallization of the desired phases was authenticated from standard ICDD card nos. 01-079-1765, 01-0830944, and 00-022-1086 for t-ZrO2, m-ZrO2, and CoFe2O4, respectively. The GSAS-EXPGUI software package was employed to refine the crystalline structures obtained from X-ray measurements, and the respective structures were acquired from the Crystallographic Information File (CIF) database. Raman spectrometry was carried out using a RENISHAW to perceive the vibrational modes of the resultant specimen using a 785 nm wavelength incident laser diode within a scan range of 200−1000 cm−1. X-ray photoelectron spectroscopy (AXIS ULTRA) is used to reveal the overall elemental composition and chemical state of the composite specimen. Binding energy calibrations were carried out by setting the value of the C 1s peak as 284.8 eV. Magnetic features were analyzed using a physical property measurement system (PPMS; Quantum Design, San Diego. CA) within the field range of ±1 T executed at room temperature. B



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Figure 1. XRD patterns of five different Co2+/Fe3+ substituted ZrO2 compositions recorded after heat treatment at 900 (a), 1100 (b), and 1300 °C (c).

tetrahedral A site in the spinel ferrite system.30−33 The Born− von Karman formalism predicts 6 Raman active modes (A1g + 2B1g + 3Eg) for t-ZrO2 polycrystals. The major vibrational modes of t-ZrO2 are determined to be ∼473 and 640 cm−1, which is assumed to get superimposed by the higher phonon energy bands of cubic CoFe2O4.34 In the case of the Raman spectra recorded at 900 and 1100 °C (Figure 2a,b), the combined existence of three distinct phases, namely, t-ZrO2, mZrO2, and CoFe2O4, was apparent in all the compositions. The presence of the dominant nature of the m-ZrO2 band exhibits good corroboration with the XRD results. 3.3. Structure Refinement. The phase fraction and lattice parameter values obtained from the refined powder XRD patterns at various temperatures are illustrated in Table 2, and the selective refined diffraction patterns are presented in Figure 3. Phase fraction data (Figure 4) obtained at three different temperatures emulate a greater significance on the stabilization capacity of both ZrO2 and CoFe2O4 structures. A gradual surge and decline in the phase content of respective t-ZrO2 and mZrO2 as a function of enhanced Co2+/Fe3+ content are obvious at every individual temperature. The comparative data of a single composition among the three different temperatures ensure a strong decline in the m-ZrO2 content with simultaneous upsurge in the t-ZrO2 phase fraction as a function of temperature

in Zr4+ revealed the presence of only m-ZrO2 at both 900 and 1300 °C. The complete absence of t-ZrO2 is witnessed in both the cases, while the minor amount reflections typical of α-Fe2O3 is witnessed in the system that possessed Co 2+ /Fe 3+ concentrations on the higher side. Further, the inability of CoFe2O4 crystallization was determined in both the systems. 3.2. Raman Spectroscopy. Raman spectra have been used to investigate the structural transition, lattice distortion, and local cation distribution in the composite system. Raman spectra recorded at 1300 °C (Figure 2c) demonstrated bands at 180, 191, 335, 383, 474, 564, and 624 cm−1 that correspond to mZrO2, t-ZrO2, and CoFe2O4. 10CFZ and 20CFZ exhibited bands at 180 and 191 cm−1 typical of m-ZrO2, and these peaks displayed a diminishing trend as a function of enhanced Co2+/ Fe3+ content.29 Nevertheless, the simultaneous existence of CoFe2O4 and t-ZrO2 is manifested from the bands determined at 474, 564, 624, and 684 cm−1. The 474 and 564 cm−1 bands are assigned to the T2g mode that arises from the asymmetric stretching of Fe−O in the octahedral site, whereas the 624 and 684 cm−1 bands represent the A1g mode that contributes from the symmetric stretching of oxygen coordination with Fe3+ and Co2+. A close analysis of the spectra unveils the existence of CoFe2O4 in the form of an inverse spinel structure where Co2+ and Fe3+, respectively, occupy the octahedral B site and C



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Figure 2. Raman spectra for five different Co2+/Fe3+ substituted ZrO2 compositions recorded after heat treatment at 900 (a), 1100 (b), and 1300 °C (c). The symbols m, t, and CF, respectively, denote m-ZrO2, t-ZrO2, and CoFe2O4.

influence this stabilization. Further, the obvious growth in the crystallite size of individual t-ZrO2 and CoFe2O4 phases has been noticed with respect to the increments in heat treatment temperature. 3.4. X-ray Photoelectron Spectroscopy. An XPS study was performed to validate the existence of multiple phases contributed by the framework of constituent elements and their corresponding oxidation states. Figure 5 displays the overall survey spectra of a specific system and their respective core level electron spectra contributed by individual elements. The XPS survey spectrum of 40CFZ (Figure 5a) envisages the presence of Fe 2p, Co 2p, O 1s, C 1s, Zr 3d, and Y 3d electronic states. The core level electron spectrum of the Fe 2p orbital (Figure 5b) with its binding energy at 710.9 and 723.8 eV is assigned to Fe 2p3/2 and Fe 2p1/2 electronic states, and the shakeup satellite peak at 718.5 eV assures the high spin Fe3+ state.35,36 Binding energy at 710.9 and 723.8 eV reveals the occurrence of Fe3+ at octahedral and tetrahedral lattices typical of a ferrite component. The core level spectrum of the Co 2p orbital (Figure 5c) displays binding energy at 779.5, 781.0, and 783.2 eV representative of Co2+ in which the 779.5 eV energy level is assigned to Co2+ in the octahedral site and 781.0 eV authenticates the occupancy of Co2+ in the tetrahedral site.37−40

increments. Moreover, the phase fraction of CoFe2O4 displayed a considerable upsurge as a function of Co2+/Fe3+ increments at a particular temperature. Likewise, a similar trend of enhanced CoFe2O4 phase content is also witnessed with respect to the temperature increments in a particular composition. At 1300 °C, the m-ZrO2 trace is still evident in 10CFZ and 20CFZ, whereas a complete withdrawal of the same has been witnessed in other compositions. The comparative lattice data of the t-ZrO2 phase in pure 8YSZ and CFZ compositions displayed considerable variations at all the temperatures. 8YSZ envisaged an expanded t-ZrO2 unit cell than all the CFZ compositions. It is noteworthy to mention that the significance of Y 3+ substitution to establish t-ZrO 2 stabilization is achieved only for the selective compositions at 1300 °C. Despite the invariable amount of 8 mol % of Y2O3 additions in all the syntheses, the results envisaged the inability to attain t-ZrO2 stabilization at 900 and 1100 °C. The expanded t-ZrO2 unit cell achieved in pure 8YSZ and the contraction of the same in all the CFZ compositions infer the inability of Y3+ accommodation at the lattice sites of ZrO2 to accomplish t-ZrO2. Still, the contracted lattice of t-ZrO2 determined in the cases of 40CFZ, 60CFZ, and 100CFZ where it possesses a unique t-ZrO2 devoid of m-ZrO2 fractions affirms the impact of Co2+/Fe3+ to D



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Table 2. Rietveld Agreement Factors, Lattice Parameters, and Crystallite Size Determined from the Refinement of Five Different CFZ Compositions Heat-Treated at 900, 1100, and 1300 °C 900 °C lattice parameters (Å) t-ZrO2

m-ZrO2

sample code

a = b axis

c axis

8YSZ 10CFZ 20CFZ 40CFZ 60CFZ 100CFZ

3.7063 (6) 3.6358(3) 3.6349(2) 3.6343(2) 3.6300(1) 3.6263(2)

5.1722 (2) 5.1584(3) 5.1569(4) 5.1550(1) 5.1500(2) 5.1479(2)

a axis

CoFe2O4

b axis

c axis

a = b = c axis

crystallite size (nm) t-ZrO2

Rietveld agreement factors

CoFe2O4

χ2

RBragg

1.55 1.16 1.40 1.55 1.20 1.08

7.12 9.62 8.74 7.98 7.67 8.93

5.1508(1) 5.1504(3) 5.1537(2) 5.1484(2) 5.1491(3)

5.1996(3) 5.1987(1) 5.2049(2) 5.2033(1) 5.2056(4) 1100 °C

5.3229(2) 5.3211(2) 5.3217(3) 5.3186(4) 5.3138(1)

8.3180(3) 8.3234(2) 8.3411(1) 8.3381(3) 8.3574(4)

49.1 51.4 69.2 59.9 48.3

55.3 72.8 35.7 72.7 54.1

5.1903(4) 5.1874(1) 5.1938(3) 5.1940(2) 5.1969(4) 1300 °C

5.3275(1) 5.3299(3) 5.3239(2) 5.3238(3) 5.3222(2)

8.3530(4) 8.3403(1) 8.3556(2) 8.3573(4) 8.3595(2)

97.7 95.6 132 125 117

78.9 70.8 85.6 74.6 88.1

1.19 1.22 1.30 1.28 1.26

7.67 9.24 8.87 7.09 9.93

148 180 162 185 220

1.16 1.40 1.55 1.20 1.08

8.31 7.36 8.01 7.22 6.63

10CFZ 20CFZ 40CFZ 60CFZ 100CFZ

3.6341(4) 3.6331(3) 3.6331(1) 3.6230(3) 3.6341(2)

5.1504 (4) 5.1480 (3) 5.1419 (2) 5.1422 (2) 5.1425 (2)

5.1518(4) 5.1517(3) 5.1489(2) 5.1492(2) 5.1489(2)

10CFZ 20CFZ 40CFZ 60CFZ 100CFZ

3.6258 (3) 3.6254 (2) 3.6232 (4) 3.6239 (3) 3.6239 (2)

5.1276 (3) 5.1372 (3) 5.1245 (3) 5.1265 (2) 5.1257 (2)

5.1562 (2) 5.1702 (3)

5.2013 (3) 5.1976 (4)

5.2931 (2) 5.3024 (3)

8.3648 (6) 8.3703 (4) 8.3682 (2) 8.3660 (3) 8.3652 (2)

153 158 181 176 196

The indentation graphs (Figure 9) revealed smooth loading and unloading profiles devoid of significant pop-ups, which ascertain the dense and pore free microstructures as determined from morphological analysis. The mechanical data (Table 3) derived from the Oliver−Pharr method discloses Young’s modulus and hardness values of 172.39 and 15.13 GPa, respectively, for 10CFZ. Thereafter, a gradual enhancement in the mechanical data is obvious as a function of enhanced Co2+/ Fe3+ additions. The maximum Young’s modulus and hardness values are achieved for 40CFZ. 3.6. Magnetic Features. Figure 10 presents the M−H curves for the different CFZ specimens measured at 300 K in the range of −1 to +1 T. A strong hysteresis loop is accomplished in the CFZ specimens, thus ensuring the ferrimagnetic characteristics. Moreover, a gradual upsurge in the magnetization value is obtained as a function of increment in the phase content of CoFe2O4 in CFZ specimens. The saturation magnetization of the thermally treated specimen displays an optimal value of 18.89 emu/g. Further, the comparably minimal magnetic coercivity values obtained from the experiment imply the soft ferrite nature of CFZ specimens.

The binding energy maximum for the Y core line doublet (Figure 5d) is positioned at 156.8 and 158.8 eV, which unveils Y 3d5/2 and Y 3d3/2 levels, respectively. The core level binding energy spectrum of the Zr 3d state (Figure 5e) exhibits a doublet at 181.8 eV (Zr 3d5/2) and 184.2 eV (Zr 3d3/2). The photoemission spectra of Zr 3d and Y 3d demonstrate a marginal chemical shift associated with the combined effect of charge transfer among Zr4+ and Y3+ alongside the Y3+ occupancy at the ZrO2 lattice inducing change in the core level binding energy.41−44 The spectrum of O 1s (Figure 5f), which is fitted with three Gaussian peaks, represents the occurrence of oxygen species associated with Zr, Fe, and Co at 529.6, 530.1, and 532.0 eV, respectively. 3.5. Morphological and Mechanical Features. Micrographs of 40CFZ and 100CFZ compositions after heat treatment at 1300 °C are shown in Figure 6a,b. Microstructures display a dense morphology contributed by the well grown grains with distinct boundaries alongside the pore free structures. Further, micrographs also unveil two different grains representative of ZrO2 and CoFe2O4 that are well recognized from their contrasting colors and morphologies. The growth of secondary grains typical of CoFe2O4 is apparent on the already crystallized ZrO2 grain. The elemental mapping results of 40CFZ and 100CFZ (Figures 7 and 8) exhibit good consistency with the morphological analysis that ensure the well distinguished t-ZrO2 and CoFe2O4 grains. Depending on the grain type and phases as determined from the XRD analysis, the distribution of constituent elements was found selective. The rich distribution of Zr4+ is apparent throughout the microstructures, except for certain specific and restricted areas, which are dominated by the presence of Co2+ and Fe3+. Yet the dispersion of Co2+ and Fe3+ traces is obvious in Zr4+ rich areas, and moreover, the scattering of Y3+ is relatively excess in Zr4+ locations rather than the Co2+/Fe3+ domains.

4. DISCUSSION The results affirm the formation of t-ZrO2/CoFe2O4 composites at 1300 °C in systems that possessed at least a minimum of 40 mol % Co2+/Fe3+ blend. Below this concentration limit, the mZrO2 trace has been determined as a tertiary product along with t-ZrO2 and CoFe2O4. Despite the invariable amount of 8 mol % Y2O3 to accomplish t-ZrO2 stabilization, the discrepancy in attained results is mainly due to the critical role imparted by Co2+/Fe3+ that are present as additional components in all the systems. It should be noted that a gradual upsurge in Co2+/Fe3+ concentrations with respect to the constant amount of Zr4+ and Y3+ has been maintained in all the syntheses. Moreover, the investigations at 900 and 1100 °C verified the invariable E



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concepts affirm the restriction displayed by the Co2+/Fe3+ content to accomplish the expected outcome. The interference of Co2+/Fe3+ with Zr4+ and Y3+ to impose contrasting structural behavior has been examined with the aid of two different experiments. The investigation performed on Co2+, Fe3+, and Y3+ mixtures devoid of Zr4+ additions validates the good affinity displayed by Y3+ toward transition metals. The products of YFeO3, YCoO3, and Y2O3 were determined in the case of Y3+ concentration higher than Co2+/Fe3+, while the vice versa specified the mixtures of YFeO3, YCoO3, and Co3O4. Thus, the availability of excess Y3+ crystallizes as Y2O3 after exceeding its saturation limit to react with Co2+ and Fe3+. The lack of sufficient Y3+ in the second case led to the precipitation of Co3O4 as an auxiliary product. Furthermore, the inability to yield CoFe2O4 in the Co2+, Fe3+, and Y3+ mixtures also becomes valuable evidence to interpret the discrepancy obtained in the system comprising Co2+, Fe3+, Y3+, and Zr4+ mixtures. The other experiment encompassing only the Co2+, Fe3+, and Zr4+ mixtures displayed the inability to attain t-ZrO2 at both 900 and 1300 °C, and further, the crystallization of α-Fe2O3 is obvious for the system that possessed a high Co2+/Fe3+ content. Moreover, the inability to determine CoFe2O4 is also inevitable. These additional experiments impart the critical role displayed by Y3+ and Zr4+ combined to retain stable CoFe2O4, while the stabilization of t-ZrO2 is highly influenced by two important factors, namely, the temperature and the concentration gradients of Co2+/Fe3+. The reverse phenomenon of an m- → t-ZrO2 phase transition persuaded by temperature increments alongside transition metals is justified from the following affirmations. At 900 °C, the presence of excess m-ZrO2 in CFZ systems is attributed to the partial occupancy of Y3+ in ZrO2 that is inadequate to attain the expected polymorph of ZrO2. It is also presumed that, at this particular temperature, the reduced m-ZrO2 content with respect to Co2+/Fe3+ increments infers the occupancy of both Y3+ and transition metals at the tZrO2 lattice. A further increment to 1100 °C also reflects a similar trend, however, with a substantial reduction in the mZrO2 content together with a further improvement in the phase content of CoFe2O4. Among the Co2+ and Fe3+ elements, the better affinity of Co2+ toward Zr4+ is confirmed from its complete dissolution in ZrO2 as witnessed in the system comprising Co2+, Fe3+, and Zr4+ mixtures. This is also justified from the lower dissolution energy possessed by cobalt (0.34 eV) rather than iron (0.62 eV). The dissolution energy of yttrium (0.34 eV) is well evident by its occupancy at the ZrO2 lattice.45 The sizes of the investigated elements, namely, Zr4+, Y3+, Co2+, and Fe3+, are, respectively, specified as 0.72, 0.90, 0.74, and 0.65 Å.46,47 Occupancy of the smaller sized Co2+ together with the larger sized Y3+ thus contributes to the contracted lattice of tZrO2 as witnessed from our results of quantitative analysis than the expanded lattice of t-ZrO2 in pure 8YSZ. It is also understood that the Co2+ to Fe3+ ratio in CoFe2O4 is 1:2, and all the experiments in the current investigation were performed with a 1:1 ratio. Hence, the availability of excess Co2+ to enter ZrO2 is also justified by the lack of individual cobalt oxide crystallization. The temperature dependent dissolution behavior of Co2+ and Fe3+ in ZrO2 is inevitable from the enhanced phase content of CoFe2O4 determined as a function of temperature increments. The dissolution is limited to low temperatures, and the upsurge in heat treatments witnessed the gradual withdrawal of Co2+ and Fe3+ from the ZrO2 lattice to ensure more CoFe2O4 formation. A handful of studies are also available to support our claim on the transition metal doped ZrO2 displaying poor ability

Figure 3. Refined X-ray diffraction patterns of selective compositions determined at 1300 °C. Panels (a) and (b) correspond to 10CFZ and 40CFZ. Panel (c) corresponds to 10CFZ at 1100 °C.

existence of m-ZrO2 in substantial amounts. Nevertheless, the gradual reduction in m-ZrO2 fraction as a function of temperature increments alongside simultaneous reduction as a function of Co2+/Fe3+ content is obvious at particular temperatures. These observations deduce the contribution of three important factors, namely, reaction kinetics, sintering temperature, and concentration gradient of Co2+/Fe3+ additives to accomplish the desired result. Further, the pure 8YSZ system devoid of Co2+/Fe3+ additives ensured the crystallization of unique t-ZrO2 at 900, 1100, and 1300 °C. The aforementioned F



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Figure 4. Phase content determined from the refinement of five different compositions heat-treated at 900 (a), 1100 (b), and 1300 °C (c).

Figure 5. XPS spectrum of 40CFZ. Panel (a) represents the overall survey spectra of 40CFZ composition. The individual core level spectra of Fe 2p, Co 2p, Y 3d, Zr 3d, and O 1s are, respectively, displayed in panels (b)−(f).

Figure 6. FE-SEM images of 40CFZ (a) and 100CFZ (b) obtained after heat treatment at 1300 °C.

ensures a gradual m- → t-ZrO2 phase transition with incremental heat treatments. At 1300 °C, the enhanced phase content of CoFe2O4 and still the minimum availability of Co2+/Fe3+ in the ZrO2 matrix are validated through elemental mapping analysis that demonstrates the maximum dispersion of Y3+ at the Zr4+

to achieve tetragonal stabilization at higher temperatures.48,49 On the other hand, the removal of Co2+ and Fe3+ also facilitates Y3+ to stabilize t-ZrO2, and hence, better stabilization capacity is determined in 40CFZ, 60CFZ, and 100CFZ systems. Further, this temperature dependent elimination of Co2+ and Fe3+ also G



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Figure 7. Elemental mapping of 40CFZ after heat treatment at 1300 °C.

Figure 8. Elemental mapping of 100CFZ after heat treatment at 1300 °C.

domains rather than its distribution at the Co2+/Fe3+ dominated areas. Further, the mapping data also certify the comparably minimum amount of Co2+/Fe3+ occupancy at the domains of Zr4+. The dense grains aided with pore free microstructures demonstrated at 1300 °C contributes for better values of hardness and Young’s modulus. A gradual improvement in mechanical properties as a function of increment in the CoFe2O4 content in the composite system is understood. Nonetheless, the relatively inferior mechanical data in the 10CFZ and 20CFZ systems is also attributed by the detection of m-ZrO2 in these compositions. The literature provides a wide range of mechanical data on ZrO2 systems that mainly depend on the type of stabilizers and processing conditions.50−53 The data on familiar ZrO2 and ZrO2 toughened Al2O3 systems that have established commercial success in hard tissue replacements are reported as 15.30 GPa.54 Other investigations also infer the mechanical data of ZrO2 and ZrO2 toughened Al2O3 systems in the range of 17.52 GPa.55 The data obtained from the current investigation establish good consistency with the already reported values. Further, the results from magnetic measurements demonstrate the ferrimagnetic characteristics of the tZrO2/CoFe2O4 system. Generally, t-ZrO2 as an individual lacks

magnetic features, and this is well reflected in the results that displayed better magnetic behavior as a function of CoFe2O4 content. In other words, CoFe2O4 as a bulk signifies exceptional magnetic features that are well demonstrated in the literature.56,57 Further, the magnetic properties of CoFe2O4 are also dependent on its size, surface area, and functionalization with a particular chemical entity.58 The relatively inferior magnetic features determined in the present system are mainly due to the bigger grain size, which is expected to possess a relatively low surface area and also its integration with the ZrO2 counterpart. Nevertheless, the attained magnetic features still possess the ability to induce appropriate heating ability to destroy cancer cells.

5. CONCLUSION The critical role of individual elements in Zr4+, Y3+, Fe3+, and Co2+ combination to yield the desired t-ZrO2/CoFe2O4 composite with varied compositional ratios has been explained. Despite the availability of a constant amount of 8 mol % Y3+, the systems fail to accomplish the expected t-ZrO2 stabilization at both 900 and 1100 °C and also at 1300 °C in certain compositions. This is mainly due to the presence of Fe3+/Co2+ in the system favoring the t- → m-ZrO2 transition at low H



Article

Figure 9. Indentation profiles of five different Co2+/Fe3+ combinations in ZrO2 system.

combined effects of the heat treatment and concentration gradient of Fe3+/Co2+. The integration of CoFe2O4 grains in the t-ZrO2 matrix is well understood from the morphological analysis, thus confirming the formation of the desired t-ZrO2/ CoFe2O4 composite. The mechanical properties derived from the indentation data of the composite system exhibit good consistency with the commercial ZrO2 implants. Further, ferrimagnetic features determined from magnetic measurements are expected to deliver sufficient heating ability to destroy tumor cells.

Table 3. Mechanical Properties Obtained from the Indentation Results of Five Different Composite Systems sample code

Young’s modulus (GPa)

hardness (GPa)

8YSZ 10CFZ 20CFZ 40CFZ 60CFZ 100CFZ

170.54 ± 5.07 172.39 ± 7.39 187.64 ± 7.62 206.78 ± 10.44 203.88 ± 8.94 189.01 ± 7.18

12.06 ± 0.24 15.13 ± 1.32 16.30 ± 1.04 18.18 ± 1.61 17.67 ± 1.36 16.43 ± 1.51

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.9b00583. Figure S1: XRD patterns for two different Co2+, Fe3+, and Y3+ combinations recorded after heat treatment at 900 and 1300 °C, respectively. Figure S2: XRD patterns for two different Co2+, Fe3+, and Zr4+ combinations recorded after heat treatment at 900 and 1300 °C, respectively (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: 0091-413-2654973. ORCID

S. Kannan: 0000-0003-2285-4907 Figure 10. Hysteresis curves derived from the VSM analysis of a varied range of Co2+/Fe3+ additions in 8 mol % Y2O3 stabilized ZrO2 system

Notes

temperatures, whereas a reverse phenomenon of an m- → t-ZrO2 transition is noticed during elevated heat treatments. The significant contribution of Fe3+/Co2+ in the system is evident as the simultaneous process of the m- → t -ZrO2 transition coupled with a progressive crystallization of CoFe2O4 is influenced by

ACKNOWLEDGMENTS The financial assistance received from the Council of Scientific and Industrial Research (CSIR) [Reference: 01(2952)/18/ EMR-II dated 01.05.2018], India, is acknowledged. The facilities availed from the Central Instrumentation Facility

The authors declare no competing financial interest.

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(15) Song, Q.; Zhang, Z. J. Shape Control and Associated Magnetic Properties of Spinel Cobalt Ferrite Nanocrystals. J. Am. Chem. Soc. 2004, 126, 6164−6168. (16) Veverka, M; Veverka, P; Kaman, O; Lancok, A; Zaveta, K; Pollert, E; Knizek, K; Bohacek, J; Benes, M; Kaspar, P; Duguet, E; Vasseur, S Magnetic Heating by Cobalt Ferrite Nanoparticles. Nanotechnology 2007, 18, 345704. (17) Habib, A. H.; Ondeck, C. L.; Chaudhary, P.; Bockstaller, M. R.; McHenry, M. E. Evaluation of Iron-Cobalt/Ferrite Core-Shell Nanoparticles for Cancer Thermotherapy. J. Appl. Phys. 2008, 103, 07A307. (18) Rana, K. S.; Souza, L. P. De; Isaacs, M. A.; Raja, F. N. S.; Morrell, A. P.; Martin, R. A. Development and Characterization of GalliumDoped Bioactive Glasses for Potential Bone Cancer Applications. ACS Biomater. Sci. Eng. 2017, 3, 3425−3432. (19) Iannotti, V.; Adamiano, A.; Ausanio, G.; Lanotte, L.; Aquilanti, G.; Coey, J. M. D.; Lantieri, M.; Spina, G.; Fittipaldi, M.; Margaris, G.; Trohidou, K.; Sprio, S.; Montesi, M.; Panseri, S.; Sandri, M.; Iafisco, M.; Tampieri, A. Fe-Doping-Induced Magnetism in Nano-Hydroxyapatites. Inorg. Chem. 2017, 56, 4446−4458. (20) Iafisco, M.; Sandri, M.; Panseri, S.; Delgado-López, J. M.; Gómez-Morales, J.; Tampieri, A. Magnetic Bioactive and Biodegradable Hollow Fe-Doped Hydroxyapatite Coated Poly(l-Lactic) Acid Micro-Nanospheres. Chem. Mater. 2013, 25, 2610−2617. (21) Iwasaki, T.; Nakatsuka, R.; Murase, K.; Takata, H.; Nakamura, H.; Watano, S. Simple and Rapid Synthesis of Magnetite/Hydroxyapatite Composites for Hyperthermia Treatments via a Mechanochemical Route. Int. J. Mol. Sci. 2013, 14, 9365−9378. (22) Inukai, A.; Sakamoto, N.; Aono, H.; Sakurai, O.; Shinozaki, K.; Suzuki, H.; Wakiya, N. Synthesis and Hyperthermia Property of Hydroxyapatite-ferrite Hybrid Particles by Ultrasonic Spray Pyrolysis. J. Magn. Magn. Mater. 2011, 323, 965−969. (23) Srdić, V. V.; Winterer, M. Aluminum-Doped Zirconia Nanopowders: Chemical Vapor Synthesis and Structural Analysis by Rietveld Refinement of X-Ray Diffraction Data. Chem. Mater. 2003, 15, 2668− 2674. (24) Corradi, A. B.; Bondioli, F.; Ferrari, A. M. Role of Praseodymium on Zirconia Phases Stabilization. Chem. Mater. 2001, 13, 4550−4554. (25) Wang, S.; Xie, H.; Lin, Y.; Poeppelmeier, K. R.; Li, T.; Winans, R. E.; Cui, Y.; Ribeiro, F. H.; Canlas, C. P.; Elam, J. W.; Zhang, H.; Marshall, C. L. High Thermal Stability of La2O3 - and CeO2 -Stabilized Tetragonal ZrO2. Inorg. Chem. 2016, 55, 2413−2420. (26) Kogler, M.; Köck, E. M.; Vanicek, S.; Schmidmair, D.; Götsch, T.; Stöger-Pollach, M.; Hejny, C.; Klötzer, B.; Penner, S. Enhanced Kinetic Stability of Pure and Y-Doped Tetragonal ZrO2. Inorg. Chem. 2014, 53, 13247−13257. (27) Sato, K.; Horiguchi, K.; Nishikawa, T.; Yagishita, S.; Kuruma, K.; Murakami, T.; Abe, H. Hydrothermal Synthesis of Yttria-Stabilized Zirconia Nanocrystals with Controlled Yttria Content. Inorg. Chem. 2015, 54, 7976−7984. (28) Guiot, C.; Grandjean, S.; Lemonnier, S.; Jolivet, J.; Batail, P. Nano Single Crystals of Yttria-Stabilized Zirconia. Cryst. Growth Des. 2009, 9, 3548−3550. (29) Yashima, M.; Ohtake, K.; Kakihana, M.; Arashi, H.; Yoshimura, M. Determination of Tetragonal-Cubic Phase Boundary of Zrl‑XRxO2‑X/2 (R = Nd, Sm, Y, Er and Yb) by Raman Scattering. J. Phys. Chem. Solids. 1996, 57, 17−24. (30) Valdés-Solís, T.; Tartaj, P.; Marbán, G.; Fuertes, A. B. Facile Synthetic Route to Nanosized Ferrites by Using Mesoporous Silica as a Hard Template. Nanotechnology 2007, 18, 145603. (31) Chandramohan, P.; Srinivasan, M. P.; Velmurugan, S.; Narasimhan, S. V. Cation Distribution and Particle Size Effect on Raman Spectrum of CoFe2O4. J. Solid State Chem. 2011, 184, 89−96. (32) Naik, S. R.; Salker, A. V.; Yusuf, S. M.; Meena, S. S. Influence of Co2+ Distribution and Spin-orbit Coupling on the Resultant Magnetic Properties of Spinel Cobalt Ferrite Nanocrystals. J. Alloys Compd. 2013, 566, 54−61. (33) da Silva, S. W.; Melo, T. F. O.; Soler, M. A. G.; Lima, E. C. D.; da Silva, M. F.; Morais, P. C. Stability of Citrate-Coated Magnetite and

(CIF) of Pondicherry University is also acknowledged. S.R. acknowledges CSIR, India (Ref. No. 09/559/0122/18-EMR-1 dated 26/04/2018), for the Senior Research Fellowship. The characterization facilities availed from IIT Bombay under INUP which is sponsored by DeitY, MCIT, Government of India, are gratefully acknowledged.

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REFERENCES

(1) Manova, E.; Kunev, B.; Paneva, D.; Mitov, I.; Petrov, L.; Estournès, C.; D’Orléan, C.; Rehspringer, J.; Kurmoo, M. Mechano-Synthesis, Characterization, and Magnetic Properties of Nanoparticles of Cobalt Ferrite, CoFe2O4. Chem. Mater. 2004, 16, 5689−5696. (2) Abdulwahab, K. O.; Malik, M. A.; O’Brien, P.; Timco, G. A.; Tuna, F.; Muryn, C. A.; Winpenny, R. E. P.; Pattrick, R. A. D.; Coker, V. S.; Arenholz, E. A One-Pot Synthesis of Monodispersed Iron Cobalt Oxide and Iron Manganese Oxide Nanoparticles from Bimetallic Pivalate Clusters. Chem. Mater. 2014, 26, 999−1013. (3) Moriya, M.; Ito, M.; Sakamoto, W.; Yogo, T. One-Pot Synthesis and Morphology Control of Spinel Ferrite (MFe2O4, M = Mn, Fe, and Co) Nanocrystals from Homo- and Heterotrimetallic Clusters. Cryst. Growth Des. 2009, 9, 1889−1893. (4) Amiri, S.; Shokrollahi, H. The Role of Cobalt Ferrite Magnetic Nanoparticles in Medical Science. Mater. Sci. Eng., C 2013, 33, 1−8. (5) Ansari, S. M.; Bhor, R. D.; Pai, K. R.; Mazumder, S.; Sen, D.; Kolekar, Y. D.; Ramana, C. V. Size and Chemistry Controlled CobaltFerrite Nanoparticles and Their Anti-Proliferative Effect against the MCF-7 Breast Cancer Cells. ACS Biomater. Sci. Eng. 2016, 2, 2139− 2152. (6) Di Guglielmo, C.; Lopez, D. R.; De Lapuente, J.; Mallafre, J. M. L.; Suarez, M. B. Embryotoxicity of Cobalt Ferrite and Gold Nanoparticles: A First in Vitro Approach. Reprod. Toxicol. 2010, 30, 271−276. (7) Casula, M. F.; Conca, E.; Bakaimi, I.; Sathya, A.; Materia, M. E.; Casu, A.; Falqui, A.; Sogne, E.; Pellegrino, T.; Kanaras, A. G. Manganese Doped-Iron Oxide Nanoparticle Clusters and Their Potential as Agents for Magnetic Resonance Imaging and Hyperthermia. Phys. Chem. Chem. Phys. 2016, 18, 16848−16855. (8) Franco, A.; E Silva, F. C. High Temperature Magnetic Properties of Cobalt Ferrite Nanoparticles. Appl. Phys. Lett. 2010, 96, 172505. (9) Alves, T. E. P.; Pessoni, H. V. S.; Franco, A., Jr. The Effect of Y3+ Substitution on the Structural, Optical Band-Gap, and Magnetic Properties of Cobalt Ferrite Nanoparticles. Phys. Chem. Chem. Phys. 2017, 19, 16395−16405. (10) Beji, Z.; Hanini, A.; Smiri, L.S.; Gavard, J.; Kacem, K.; Villain, F.; Greneche, J.-M.; Chau, F.; Ammar, S. Magnetic Properties of ZnSubstituted MnFe2O4 Nanoparticles Synthesized in Polyol as Potential Heating Agents for Hyperthermia. Evaluation of Their Toxicity on Endothelial Cells. Chem. Mater. 2010, 22, 5420−5429. (11) Levy, M.; Quarta, A.; Espinosa, A.; Figuerola, A.; Wilhelm, C.; García-Hernández, M.; Genovese, A.; Falqui, A.; Alloyeau, D.; Buonsanti, R.; Cozzoli, P. D.; García, M. A.; Gazeau, F.; Pellegrino, T. Correlating Magneto-Structural Properties to Hyperthermia Performance of Highly Monodisperse Iron Oxide Nanoparticles Prepared by a Seeded-Growth Route. Chem. Mater. 2011, 23, 4170− 4180. (12) del Real, R. P.; Arcos, D.; Vallet-Regí, M. Implantable Magnetic Glass-Ceramic Based on (Fe,Ca)SiO3 Solid Solutions. Chem. Mater. 2002, 14, 64−70. (13) Pradhan, P.; Giri, J.; Samanta, G.; Sarma, H. D.; Mishra, K. P.; Bellare, J.; Banerjee, R.; Bahadur, D. Comparative Evaluation of Heating Ability and Biocompatibility of Different Ferrite-Based Magnetic Fluids for Hyperthermia Application. J. Biomed. Mater. Res., Part B 2007, 81B, 12−22. (14) Smolkova, I. S.; Kazantseva, N. E.; Babayan, V.; Vilcakova, J.; Pizurova, N.; Saha, P. The Role of Diffusion-Controlled Growth in the Formation of Uniform Iron Oxide Nanoparticles with a Link to Magnetic Hyperthermia. Cryst. Growth Des. 2017, 17, 2323−2332. J



Article

Progressive Yttrium Additions. J. Phys. Chem. Solids 2018, 112, 100− 105. (54) De Aza, A. H.; Chevalier, J.; Fantozzi, G.; Schehl, M.; Torrecillas, R. Crack Growth Resistance of Alumina, Zirconia and Zirconia Toughened Alumina Ceramics for Joint Prostheses. Biomaterials 2002, 23, 937−945. (55) Liu, J.; Yan, H.; Reece, M. J.; Jiang, K. Toughening of Zirconia/ Alumina Composites by the Addition of Graphene Platelets. J. Eur. Ceram. Soc. 2012, 32, 4185−4193. (56) Maaz, K.; Mumtaz, A.; Hasanain, S. K.; Ceylan, A. Synthesis and Magnetic Properties of Cobalt Ferrite (CoFe2O4) Nanoparticles Prepared by Wet Chemical Route. J. Magn. Magn. Mater. 2007, 308, 289−295. (57) Sato, T.; Iijima, T.; Seki, M.; Inagaki, N. Magnetic Properties of Ultrafine Ferrite Particles. J. Magn. Magn. Mater. 1987, 65, 252−256. (58) El-Okr, M. M.; Salem, M. A.; Salim, M. S.; El-Okr, R. M.; Ashoush, M.; Talaat, H. M. Synthesis of Cobalt Ferrite Nano-Particles and Their Magnetic Characterization. J. Magn. Magn. Mater. 2011, 323, 920−926.

Cobalt-Ferrite Nanoparticles: A Raman Spectroscopy Investigation. IEEE Trans. Magn. 2003, 39, 2645−2647. (34) Ghosh, A.; Suri, A. K.; Pandey, M.; Thomas, S.; Rama Mohan, T. R.; Rao, B. T. Nanocrystalline Zirconia-Yttria System-a Raman Study. Mater. Lett. 2006, 60, 1170−1173. (35) Devaiah, D.; Smirniotis, P. G. Effects of the Ce and Cr Contents in Fe-Ce-Cr Ferrite Spinels on the High-Temperature Water-Gas Shift Reaction. Ind. Eng. Chem. Res. 2017, 56, 1772−1781. (36) Damma, D.; Boningari, T.; Smirniotis, P. G. High-Temperature Water-Gas Shift over Fe/Ce/Co Spinel Catalysts: Study of the Promotional Effect of Ce and Co. Mol. Catal. 2018, 451, 20−32. (37) Zhao, L.; Zhang, H.; Xing, Y.; Song, S.; Yu, S.; Shi, W.; Guo, X.; Yang, J.; Lei, Y.; Cao, F. Studies on the Magnetism of Cobalt Ferrite Nanocrystals Synthesized by Hydrothermal Method. J. Solid State Chem. 2008, 181, 245−252. (38) Gu, Z.; Xiang, X.; Fan, G.; Li, F. Facile Synthesis and Characterization of Cobalt Ferrite Nanocrystals via a Simple Reduction-Oxidation Route. J. Phys. Chem. C 2008, 112, 18459− 18466. (39) Mohapatra, S.; Rout, S. R.; Maiti, S.; Maiti, T. K.; Panda, A. B. Monodisperse Mesoporous Cobalt Ferrite Nanoparticles: Synthesis and Application in Targeted Delivery of Antitumor Drugs. J. Mater. Chem. 2011, 21, 9185. (40) Zhang, Z.; Li, W.; Zou, R.; Kang, W.; San Chui, Y.; Yuen, M. F.; Lee, C.-S.; Zhang, W. Layer-Stacked Cobalt Ferrite (CoFe2O4) Mesoporous Platelets for High-Performance Lithium Ion Battery Anodes. J. Mater. Chem. A 2015, 3, 6990−6997. (41) Theunissen, G. S. A. M.; Winnubst, A. J. A.; Burggraaf, A. J. Surface and Grain Boundary Analysis of Doped Zirconia Ceramics Studied by AES and XPS. J. Mater. Sci. 1992, 27, 5057−5066. (42) Tsunekawa, S.; Asami, K.; Ito, S.; Yashima, M.; Sugimoto, T. XPS Study of the Phase Transition in Pure Zirconium Oxide Nanocrystallites. Appl. Surf. Sci. 2005, 252, 1651−1656. (43) Hernandez, M. T.; Jurado, J. R.; Duran, P.; Fierro, J. L. G. Subeutectoid Degradation of Yttria-Stabilized Tetragonal Zirconia Polycrystal and Ceria-Doped Yttria-Stabilized Tetragonal Zirconia Polycrystal Ceramics. J. Am. Ceram. Soc. 1991, 74, 1254−1258. (44) Zhang, Y.; Zhang, L.; Deng, J.; Dai, H.; He, H. Controlled Synthesis, Characterization, and Morphology-Dependent Reducibility of Ceria-Zirconia-Yttria Solid Solutions with Nanorod-like, Microspherical, Microbowknot-like, and Micro-Octahedral Shapes. Inorg. Chem. 2009, 48, 2181−2192. (45) Meredig, B.; Wolverton, C. Dissolving the Periodic Table in Cubic Zirconia: Data Mining to Discover Chemical Trends. Chem. Mater. 2014, 26, 1985−1991. (46) Shannon, R. D. Revised Effective Ionic Radii and Systematic Studies of Interatomie Distances in Halides and Chaleogenides. Acta Crystallogr. 1976, A32, 751. (47) Shannon, R. D.; Prewitt, C. T. Effective Ionic Radii in Oxides and Fluorides. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1969, 25, 925−946. (48) Figueroa, S.; Desimoni, J.; Rivas, P. C.; Cervera, M. M.; Caracoche, M. C.; de Sanctis, O. Hyperfine Study on Sol-Gel DerivedHematite Doped Zirconia. Chem. Mater. 2005, 17, 3486−3491. (49) Ghigna, P.; Spinolo, G.; Anselmi-Tamburini, U.; Maglia, F.; Dapiaggi, M.; Spina, G.; Cianchi, L. Fe-Doped Zirconium Oxide Produced by Self-Sustained High-Temperature Synthesis: Evidence for an Fe-Zr Direct Bond. J. Am. Chem. Soc. 1999, 121, 301−307. (50) Mangalaraja, R.; Chandrasekhar, B.; Manohar, P. Effect of Ceria on the Physical, Mechanical and Thermal Properties of Yttria Stabilized Zirconia Toughened Alumina. Mater. Sci. Eng., A 2003, 343, 71−75. (51) Ponnilavan, V.; Kannan, S. Dy3+ occupancy in Zirconia Lattice Affects Tetragonal to Cubic Phase Transitions in Zirconia Toughened Alumina Systems. Cryst. Growth Des. 2017, 17, 127−134. (52) Vasanthavel, S.; Kannan, S. Phase Stabilization of ZrO2 Polymorph by Combined Additions of Ca 2+ and PO43‑ Ions through an in Situ Synthetic Approach. J. Am. Ceram. Soc. 2014, 97, 3774−3780. (53) Vasanthavel, S.; Kannan, S. Structural Investigations on the Tetragonal to Cubic Phase Transformations in Zirconia Induced by K


CoFe2O4 Composite

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