Oxide Crystal Structure with Square-Pyramidally Coordinated

Research Article pubs.acs.org/journal/ascecg

Oxide Crystal Structure with Square-Pyramidally Coordinated Vanadium for Integrated Electronics Manufactured at Ultralow Processing Temperatures Matjaz Valant,*,†,‡ Jasminka Popović,§ Mojca Vrčon Mihelj,‡ Sanja Burazer,§ Angela Altomare,∥ and Anna Moliterni∥ †

Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, No. 4, Section 2, North Jianshe Road, Chengdu 610054, China ‡ Materials Research Laboratory, University of Nova Gorica, Vipavska 13, 5000 Nova Gorica, Slovenia § Laboratory for Synthesis and Crystallography of Functional Materilas, Center of Excellence for Advanced Materials and Sensing Devices, Division for Materials Physics, Rudjer Boskovic Institute, Bijenička cesta 54, 10000 Zagreb, Croatia ∥ Istituto di Cristallografia, CNR, Sede di Bari, Via G. Amendola 122/o, 70126 Bari, Italy ABSTRACT: The study describes a targeted synthesis of a new dielectric material for an emerging ULTCC-I technology (ultralow temperature co-fired ceramic technology), which resulted in discovery of a PbTeV2O8 phase. A structural solution from powder data showed that the phase belongs to no known crystallographic family and is formed from V5+ ions in an unusual square-pyramidal coordination. It is characterized by very low processing temperatures that enable integration with Al electrodes and, potentially, even with polymer and paper substrates. Dielectric properties in combination with processing parameters qualify the PbTeV2O8 phase for integration, as midpermittivity capacitors, in ULTCC-I modules. KEYWORDS: Vanadate, Tellurium oxide, ULTCC, Aluminum electrode, Co-sintering

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INTRODUCTION

Since the quest for ULTCC-I materials has only been proclaimed recently and the required processing properties are so stringent, only a few of such materials have been identified so far. A new spinel-like NaAgMoO4 compound with permittivity (ε′) of 7.9 has been developed. It can be sintered at 400 °C and is fully compatible with base electrode metals such as Ag and Al. However, due to its expensive composition, use in low-cost consumer electronics is not feasible. Processing of Li2MoO4 has been improved in a way that allows its densification to about 93% relative density with application of moderate uniaxial pressure of 180 MPa and thermal post-treatment at 120 °C.8 The permittivity of such ceramics is around 5 but can be increased to around 10 by high permittivity additives.9 A special group of ULTCC-I materials are dielectric inks such as colloidal SiO2 and ZrSiO2 dielectric inks that do not need any thermal treatment.10,11 These systems cannot be considered as fully inorganic. Due to the presence of organic binders and other organic additives, the printed layers after curing contain ceramic particles distributed within a polymer

Within the last decades, the technological and scientific importance of vanadates has rapidly increased due to their fascinating functional properties that are well suited for upcoming advanced technologies. They are highly efficient materials for photoelectrochemical energy conversion,1,2 as fast oxide ion conductors for solid fuel cells3,4 or electrode material for lithium batteries.5 Another technology area, where vanadates are becoming the material of choice, is electronics. Vanadates have already been applied as passive electronic components for integration on inorganic substrates that require modest processing temperatures or with low-melting metal electrodes (so-called low and ultralow temperature co-fired ceramicsLTCC and ULTCC).6 For instance, for the ULTCC technology, processing temperatures less than 650 °C are required for integration with semiconductor, metal, or some glass substrates. However, recent trends in integrated electronics are going toward flexible organic or even paper substrates and metal inks that cannot tolerate such processing temperatures. It is becoming increasingly important to develop yet another generation of electronic materials that can be processed at temperatures less than 450 °C. This is a so-called category I of ULTCC or ULTCC-I.7 © 2017 American Chemical Society

Received: December 20, 2016 Revised: May 17, 2017 Published: May 25, 2017 5662

DOI: 10.1021/acssuschemeng.6b03111 ACS Sustainable Chem. Eng. 2017, 5, 5662−5668

Research Article

ACS Sustainable Chemistry & Engineering

PbTeV2O8 stoichiometry. However, published lists of diffraction lines for either of the two polymorphs completely disagree with a diffraction pattern of the compound of the same stoichiometry that we synthesized. The reason for the disagreement is yet unknown. So, in this paper, we give our solution of the crystal structure based on our diffraction pattern. We determine a level of nonstoichiometry and main phase relations. The processing characteristics of the ceramics, dielectric properties, and chemical compatibility with base metals are analyzed in order to demonstrate its applicability in the ULTCC-I technology.

matrix. In general, these inks are low-permittivity dielectric systems with ε′ < 5. Low-permittivity glasses have also been developed with the processing temperature around 300 °C,12 but glass−ceramic composites provide more flexibility in terms of tuning the dielectric properties to requirements of a particular electronic component. B2O3−Bi2O3−SiO2−ZnO glass has been proven as an efficient matrix for the glass− ceramic systems that can be sintered in a range from 400 to 450 °C. The tuning can be achieved by variation in glass content and dielectric properties of the ceramic fillers such as Al2O3 and BaTiO313,14 Parallel to the research on new materials, new sintering techniques have been developed. Among them, a so-called cold sintering process has recently been demonstrated with very prosperous results.15−17 A number of compounds have been compacted into dense ceramics by the addition of a small amount of water that induces the dissolution−precipitation process and enhances diffusion required for the sintering to occur. The ceramics prepared by this approach reached 85− 98% relative density after a heat treatment at temperatures less than 300 °C and application of uniaxial pressure. Apart from the glass−ceramic systems with very complex phase composition and microstructure, no other ceramic material exists with the permittivity high enough (>20) for capacitor applications in ULTCC-I technologies. A number of known compositions, majority from vanadate, molibdate, tungstate, tellurate, and borate systems, has been studied so far for the mid/high permittivity capacitor application; however, none of them exhibits the sintering temperature low enough for the ULTCC-I technology. There is an obvious need for a targeted design and synthesis of new compounds that would satisfy the stringent processing and dielectric requirement of this technology. In the quest for new ULTCC-I materials, we have focused on the PbO−TeO2−V2O3 system to explore the vanadates in combination with other high-diffusive elements. Within this system, we discovered a new PbTeV2O8 compound that can, according to its processing and dielectric properties, be applied as a capacitor in the ULTCC-I technology. In addition, the compound is also interesting due to its crystallographic features. Its low-symmetry crystal structure appears to have no existing isostructural analogues. Another peculiarity is that the V5+ ions in this crystal structure are in square-pyramidal coordination geometry. The square pyramidal coordination of transition metal ions in inorganic oxide compounds is very rare. It occurs around V5+ ions in the α-V2O5 crystal structure where five oxygen ions, coordinated on a distance from 1.54 to about 2 Å, form the square pyramid. The sixth oxygen is very weakly bound on a distance of over 2.8 Å and cannot be considered as a part of the coordination polyhedron.18 The square-pyramidal geometry also occurs in a variety of other vanadium oxide frameworks that were systematically reviewed by Zavalij and Whittingham.19 In β-TeVO4, V4+ ions are also stable in coordination geometry very similar to that in the α-V2O5 crystal structure.20 Recently, the TeVO4 compound has been under an intensive investigation due to its unusual spin-stripe antiferromagnetic structure induced in separated zigzag chains of the V4+ edge-sharing square pyramids that contain uncoupled spins.21,22 There are no previous reports on the newly discovered PbTeV2O8 compound apart from an old study published in ref 23. In this study, the authors described the PbO−TeO2−V2O5 ternary system and two polymorphs that correspond to the

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EXPERIMENTAL SECTION

Synthesis and Characterization. The samples with a composition of Pb1−xTeV2O8−x (0 ≤ x < 0.1) were synthesized by a solid-state reaction method. High purity PbO (99.9%), TeO2 (99.9%), and V2O5 (99.6%) were homogenized in a planetary mill in ethanol medium at 400 rpm for 2 h. The dried powder was pressed and fired in air at 400 °C for 2 h with 8 °C/min heating and cooling rates. After firing, the pellets were crushed and thoroughly ground in the planetary mill under the same conditions as before. The dried powders were pressed into pellets and sintered in air at 420−460 °C for 2 h. The synthesis was highly reproducible and always gave the same XRD pattern. For the phase analysis, the X-ray diffraction (XRD) patterns were taken by Rigaku MiniFlex 600 diffractometer in reflection (Bragg− Brentano) mode using Cu Kα radiation. Data were collected on a high-speed 1D silicon strip D/teX Ultra 250 detector in a range of 10° ≤ 2θ ≤ 80° with a scan step of 0.02° and counting speed 10°/min. For the structure solution and refinement, diffraction data were taken at room temperature in a range of 10° ≤ 2θ ≤ 120° with a scan step of 0.01° and scan speed 2°/min. Microstructural studies and elemental mapping were performed with a Jeol JSM 7001 TTLS scanning electron microscope equipped with an X-MaxN Oxford Instruments energy dispersive X-ray (EDX) detector. Melting point was determined with a TGA/DSC 2 Mettler Toledo thermal analyzer. Dielectric measurements were performed on densely sintered ceramic pellets, metalized with silver paste on an Agilent E4980A Precision LCR meter. For the temperature dependence measurements, they were mounted in a cryocooler and a heating chamber. Structure Solution and Refinement. The structure of PbTeV2O8 has been solved by the program EXPO.24 For the structure solution, a reduced diffraction pattern (up to 2Θ = 103.77°) was used. The indexing procedure was performed via the program NTREOR09.25 The space group determination step26−28 was carried out via a statistical analysis based on the integrated intensities extracted by decomposing the experimental pattern into single diffraction intensities via the Le Bail algorithm.29 It was revealed that the most probable extinction group was P121/a1, and the corresponding space group P21/a was selected for the next steps of structure solution. At the end of the full pattern decomposition process, the integrated intensities were submitted to Direct Methods.30 Once the normalization process was carried out, the strongest reflections were selected and involved in the calculation of the triplet invariants relationships whose phases were estimated by the P10 formula.31 At the end of the phasing step, many plausible sets of phases were available, whose reliability was assessed by the combined figure of merit (CFOM).32 Here, 20 sets of phases with the largest CFOM values were stored by EXPO. All the sets of phases were explored by EXPO. The electron density map corresponding to set no. 3 resulted in most chemically meaningful model, so it was chosen for further structure model optimization and refinement. Rietveld refinement was carried out in HighScore Xpert 4.5 by using a Pseudo-Voight profile function in the 2Θ range up to 120°. During the refinement zero shift, scale factor, half-width (U, V, W), peak shape parameters, unit-cell constants, atomic coordinates, and thermal parameters were simultaneously refined. Occupancy parameters were refined separatly in order to avoid the possible correlation with thermal parameters. 5663

DOI: 10.1021/acssuschemeng.6b03111 ACS Sustainable Chem. Eng. 2017, 5, 5662−5668

Research Article

ACS Sustainable Chemistry & Engineering

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Crystal Structure. A structural refinement was performed based on a diffraction pattern of the single phase Pb0.97TeV2O7.97 (hereafter addressed as PbTeV2O8 phase). The PbTeV2O8 phase crystallizes in a monoclinic system in the centrosymmetric P21/a space group (no. 14) and unit cell parameters a = 13.3526(1) Å, b = 9.05670(7) Å, c = 5.26869(4) Å, and β = 93.9645(1)o. Graphical results of the Rietveld structural refinement are shown in Figure 2. The good

RESULTS AND DISCUSSION Stoichiometry and Phase Relations. Studying the PbO− TeO2−V2O5 ternary system, we have discovered presence of a new phase with a yet unknown diffraction pattern and a stoichiometry close to PbTeV2O8. A backscattered electron analysis showed that a nominally stoichiometric composition does not yield a single PbTeV2O8 phase (Figure 1). A

Figure 2. Rietveld refinement of PbTeV2O8 phase. Experimental data are given as a red line, calculated profile is shown in blue, while the difference curve is given below the pattern. Inset shows an enlarged part of the pattern in a range 8°−52° confirming no unidentified diffraction lines.

agreement between the observed and calculated patterns unambiguously confirms the formation of the PbTeV2O8 phase. Crystal data and a summary of the structure refinement are listed in Table 1; the atomic coordinates, occupancies, and thermal parameters are given in Table 2. CIF is deposited in CSD under no. CCDC 1511279. The unit-cell of the PbTeV2O8 phase contains 12 atoms in an asymmetric unit, one Pb, one Te, two V, and eight O, all located on the 4e Wyckhof position. Both vanadium atoms are coordinated by five oxygen atoms, thus forming VO5 polyhedra Figure 1. Phase analysis of PbTeV2O8 phase: XRD diffraction patterns of powders with a nominal composition corresponding to Pb1−xTeV2O8−x and corresponding backscatter electron images of microstructures taken by SEM. Light secondary phase in the microstructure of x = 0 sample (marked with # on the XRD pattern) is the new Pb2TeV2O9 phase, and dark grain-boundary phase (marked with ∗ on the XRD pattern) in the x = 0.10 samples is Te2V2O9..

Table 1. Crystal Data and Summary of Structure Refinement of PbTeV2O8 Phase

secondary phase has been detected, for which the EDX analysis gave a stoichiometry of Pb2TeV2O9. This phase has also not been described yet; however, its analysis is beyond the scope of this paper. Since the secondary phase is low on Te, we initially checked if any mass loss had occurred during the synthesis. A TG analysis confirmed that no mass had been lost, which indicates that the PbTeV2O8 phase is not ideally stoichiometric but rather Pb deficient. For this reason we synthesized a series of compositions with a different substoichiometry of Pb according to Pb1−xTeV2O8−x and a compositional step x = 0.01. The syntheses yielded a single-phase product for x = 0.03, which gives stoichiometry of Pb0.97TeV2O7.97. Consequently, a set of diffraction lines that obviously belong to Pb2TeV2O9 (lines at 2Θ = 15.2°, 17.8°, 25.1°) disappeared from the XRD pattern. For Pb-deficient compositions corresponding to higher x values, another set of diffraction lines that belong to Te2V2O9 appeared. 5664

profile function

pseudo-Voigt

R (profile)/% R (weighted profile)/% GOF d-statistic formula sum formula sum formula mass/g/mol F(000) space group lattice parameters a/Å b/Å c/Å β/deg R (Bragg)/% scale factor U V W shape parameter

5.709 7.739 1.75 0.264 Pb0.97TeV2 O7.97 Pb3.88Te4.00V8.00O31.87 2238.5210 967.7834 P 1 21/a 1 13.3526(1) 9.05670(7) 5.26869(4) 93.9645(1) 2.45473 0.0001537(1) 0.022(1) 0.009(1) 0.0154(2) 0.574(3) DOI: 10.1021/acssuschemeng.6b03111 ACS Sustainable Chem. Eng. 2017, 5, 5662−5668

Research Article

ACS Sustainable Chemistry & Engineering Table 2. Refined Atomic Coordinates, Occupancies, and Thermal Parameters for Pb0.97TeV2 O7.97 atom

x

y

z

Uiso

occupancy

Pb1 Te1 V1 V2 O2 O3 O4 O6 O7 O8 O9 O10

0.10035(5) 0.08998(7) 0.8459(2) 0.1725(2) 0.2746(5) 0.0507(5) 0.9113(6) 0.7366(5) 0.1704(6) 0.0769(5) 0.9553(5) 0.8374(6)

0.16725(6) 0.71572(8) 0.5792(2) 0.8978(2) 0.8489(6) 0.8262(8) 0.5847(7) 0.6398(6) 0.0764(8) 0.8634(7) 0.6647(7) 0.4032(7)

0.2200(1) 0.2458(2) 0.2949(4) 0.7365(5) 0.942(1) 0.531(1) 0.579(1) 0.413(1) 0.745(2) 0.983(1) 0.112(1) 0.255(1)

0.018(3) 0.016(9) 0.019(6) 0.019(3) 0.031(3) 0.032(5) 0.035(7) 0.023(7) 0.030(7) 0.028(8) 0.029(3) 0.027(3)

0.972(9) 1.000(7) 1.000(7) 1.000(9) 1.000(8) 1.000(8) 0.996(8) 1.000(9) 0.971(9) 1.000(8) 1.000(8) 1.000(8)

Figure 3. Crystal structure of the PbTeV2O8 phase in the P21/a space group. Pb and Te atoms are represented by gray and gold balls, respectively, while V coordination polyhedra are given in purple. Pb and Te coordination polyhedra are omitted for clarity.

Processing of PbTeV 2 O 8 Ceramics for ULTTC-I Technology. The melting point of the compound was analyzed by DSC and determined to be 462 °C (Figure 4).

that are connected in a corner-sharing manner to form 1-D zigzag chains parallel to the c axis (Figure 3). The coordination around the vanadium ions, V1 and V2, can be described as a distorted square pyramid with one apical bond distance (V1− O10 = 1.61(1) Å and V2−O7 = 1.62(2) Å) being shorter than other four and corresponding to the double bond. The vanadium chains are mutually interconnected via isolated TeO4 and PbO3 polyhedra forming 2-D layers in the ac plane. Tellurium forms a very distorted TeO4 polyhedra; however, if the lone electron pair of Te4+ cation is taken into account, then the TeO4 coordination polyhedron can be described as a distorted trigonal bypiramid, where the angle between axial O6−Te1−O9 bonds is 161.5(1)° and the angle between equatorial O8−Te1−O3 bonds is 100.7 (4)°. Similarly, if the lone electron pair is considered in the case of lead, the coordination sphere could be described as a very distorted tetrahedra. During the Rietveld refinement, the occupancy parameters of all metal sites (Pb1, Te1, V1, and V2) and all eight oxygen positions were refined. The refinement showed a decrease in the occupancy parameters for the Pb1 and O7 sites, whereas Te1, V1, V2, and remaining seven oxygen positions remained fully occupied. It is important to point out that the occupancy parameters of Pb1 and all oxygen sites were not mutually constrained in any way. No charge balance requirements were imposed, yet the refined values of the occupancy parameters are chemically meaningful. The final formula of the compound, as derived from the refinement on XRPD data, was found to be Pb0.97TeV2O7.97. It shows the Pb and O deficiency that is consistent with that one found by the EDX analysis.

Figure 4. Thermal analysis of the PbTeV2O8 phase showing an endothermic DSC peak corresponding to melting (black line); heating rate of 1 °C. During the melting no mass change was observed on the TG plot (blue line).

This extraordinary low melting point determines a sintering temperature that, consequently, is expected to be within the ULTCC-I range. Figure 5 shows relative densities of the PbTeV2O8 ceramics sintered from the ball-milled powder with a mean particle size of 0.7 μm. The ceramics with 95% relative density was obtained after sintering at 440 °C. The microstructure is composed of about micron-sized grains with no secondary or grain-boundary phase observed. It is reasonable to expect that by using the powder with even smaller particle size, which can be produced by various wet chemistry methods, the sintering temperature can be further 5665

DOI: 10.1021/acssuschemeng.6b03111 ACS Sustainable Chem. Eng. 2017, 5, 5662−5668

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ACS Sustainable Chemistry & Engineering

a perfectly localized Al concentration, which indicates that Al does not even diffuse along the grain boundaries or into the bulk of the PbTeV2O8 grains. This is important in order to avoid increasing leakage current and decreasing insulation resistance in the integrated thin film modules. Dielectric Properties. The permittivity and dielectric losses of the PbTeV2O8 phase were measured in a wide temperature range from 20 to 500 K. In the entire range, we see no dielectric anomalies that would indicate a phase transition of any kind (Figure 7). This corresponds to the DSC measure-

Figure 5. Relative densities of the PbTeV2O8 ceramics after sintering at various temperatures for 1 h and a SEM image of a microstructure of the ceramics sintered to 95% of the theoretical density at 450 °C. Inset shows a thermally etched microstructure after sintering 2 h at 440 °C.

reduced. However, the purpose of our study, performed with the powder that was just milled in a planetary mill, was to show that, even with this facile technique, the low sintering temperature gives high density ceramics. Since in the ULTCC technology the ceramics is co-sintered with metal electrodes, they must be mutually chemically compatible. Because of its suitable melting point and good conductivity, Ag is often used despite been costly. However, for the ULTCC-I technology, Al is the electrode metal of choice because it is much cheaper and its melting point is still high enough (660 °C) despite been relatively low for a metal. We checked the compatibility by co-sintering the Ag and Al powders together with the PbTeV2O8 powder at 440 °C. Under these conditions, silver has completely reacted with PbTeV2O8, while aluminum did not react. The XRD pattern after the heat treatment showed nothing else than diffraction peaks of PbTeV2O8 and Al (Figure 6). The elemental mapping showed

Figure 7. Temperature and frequency dependence of relative permittivity and dielectric losses of the PbTeV2O8 ceramics. Dashed line shows the change in the measurements system from cryogenic to high temperature.

ments, which confirmed the absence of any phase transition up to the melting point (Figure 4) and indicates that the PbTeV2O8 phase with its centrosymmetric crystal structure is paraelectric in the entire range. The dielectric losses (tan δ, measured at 1 MHz) at cryogenic temperatures are in an order of 10−4 and increase at room temperature to 9 × 10−3 that still represents a low value for ULTCC dielectrics. The relative permittivity at room temperature was measured to be 21.4, and a temperature coefficient of permittivity in a linear range between 100 to 300 K was calculated to be 250 ppm/K. At higher temperatures and low frequencies, an increase in the permittivity and dielectric losses shows a thermally induced increase in conductivity. The room temperature permittivity is only slightly lower than a permittivity calculated by the Clausius−Mosotti equation from the Shannon’s ion dielectric polarizabilities using the polarizability additive rule.33 The calculated permittivity value is 25.0. Such a rather small discrepancy shows on a relatively compact crystal structure without significant ion compression or rattling, which would through excessive lattice dynamics or stress increase structural instability and dielectric loss.

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CONCLUSIONS As an emerging advance technology, ULTTC-I suffers from a lack of suitable dielectric materials. The stringent requirements of the ULTCC-I technology require a targeted design of the new materials. Such an approach resulted in discovery of a PbTeV2O8 phase. Our studies showed that a crystal structure of the PbTeV2O8 phase belongs to no known structural family. Unusual square-pyramidal coordination around V5+ was found

Figure 6. XRD pattern of a mixture of Al and PbTeV2O8 powders after heat treatment at 440 °C for 1 h is compared to an XRD pattern of pure PbTeV2O8 processed under the same conditions. The difference in the patterns only shows diffraction lines of Al. In the right upper corner, EDX elemental mapping confirms the full chemical compatibility of the phases. 5666

DOI: 10.1021/acssuschemeng.6b03111 ACS Sustainable Chem. Eng. 2017, 5, 5662−5668

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(9) Kähäri, H.; Teirikangas, M.; Juuti, J.; Jantunen, H. Improvements and Modifications to Room-Temperature Fabrication Method for Dielectric Li2MoO4 Ceramics. J. Am. Ceram. Soc. 2015, 98, 687−689. (10) Varghese, J.; Surendran, K. P.; Sebastian, M. T. Room Temperature Curable Silica Ink. RSC Adv. 2014, 4, 47701−47707. (11) Varghese, J.; Teirikangas, M.; Puustinen, J.; Jantunen, H.; Sebastian, M. T. Room Temperature Curable Zirconium Silicate Dielectric Ink for Electronic Applications. J. Mater. Chem. C 2015, 3, 9240−9246. (12) Varghese, J.; Siponkoski, T.; Teirikangas, M.; Sebastian, M. T.; Uusimäki, A.; Jantunen, H. Structural, Dielectric, and Thermal Properties of Pb Free Molybdate Based Ultralow Temperature Glass. ACS Sustainable Chem. Eng. 2016, 4, 3897−3904. (13) Chen, M.-Y.; Juuti, J.; Hsi, C.-S.; Chia, C.-T.; Jantunen, H. Dielectric Properties of Ultra-Low Sintering Temperature Al2O3− BBSZ Glass Composite. J. Am. Ceram. Soc. 2015, 98, 1133−1136. (14) Chen, M.-Y.; Juuti, J.; Hsi, C.-S.; Chia, C.-T.; Jantunen, H. Dielectric BaTiO3−BBSZ Glass Ceramic Composition with Ultra-Low Sintering. J. Eur. Ceram. Soc. 2015, 35, 139−144. (15) Guo, J.; Guo, H.; Baker, A. L.; Lanagan, M. T.; Kupp, E. R.; Messing, G. L.; Randall, C. A. Cold Sintering: A Paradigm Shift for Processing and Integration of Ceramics. Angew. Chem., Int. Ed. 2016, 55, 11457−11461. (16) Guo, H.; Baker, a.; Guo, J.; Randall, C. A. Cold Sintering Process for Low-Temperature Ceramic Processing of Ferroelectrics. J. Am. Ceram. Soc. 2016, 99, 3489−3507. (17) Guo, J.; Berbano, S. S.; Guo, H.; Baker, A. L.; Lanagan, M. T.; Randall, C. A. Cold Sintering Process of Composites: Bridging the Processing Temperature Gap of Ceramic and Polymer Material. Adv. Funct. Mater. 2016, 26, 7115−7121. (18) Byström, A.; Wilhelmi, K.-A.; Brotzen, O. Vanadium Pentoxide a Compound with Five-Coordinated Vanadium Atoms. Acta Chem. Scand. 1950, 4, 1119−1130. (19) Zavalij, P. Y.; Whittingham, M. S. Structural Chemistry of Vanadium Oxides with Open Frameworks. Acta Crystallogr., Sect. B: Struct. Sci. 1999, 55, 627−663. (20) Meunier, G.; Darriet, J.; Galy, J. L’Oxyde Double TeVO4 II. Structure Cristalline de TeVO4-β-Relations Structurales. J. Solid State Chem. 1973, 6, 67−73. (21) Saúl, A.; Radtke, G. Density Functional Approach for the Magnetism of β-TeVO4. Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 89, 104414. (22) Pregelj, M.; Zorko, A.; Zaharko, O.; Nojiri, H.; Berger, H.; Chapon, L. C.; Arčon, D. Spin-Stripe Phase in a Frustrated Zigzag Spin-1/2 Chain. Nat. Commun. 2015, 6, 7255. (23) Sveshtarova, P. G.; Stavrakeva, D. A.; Marlinov, M. R. Phase Equilibrium in the PbO-TeO2-V2O5 System. Doklady Bolgarskoi Akademii Nauk 1981, 34, 1671−1674. (24) Altomare, A.; Cuocci, C.; Giacovazzo, C.; Moliterni, A.; Rizzi, R.; Corriero, N.; Falcicchio, A. EXPO2013: a kit of tools for phasing crystal structures from powder data. J. Appl. Crystallogr. 2013, 46, 1231−1235. (25) Altomare, A.; Campi, G.; Cuocci, C.; Eriksson, L.; Giacovazzo, C.; Moliterni, A.; Rizzi, R.; Werner, P.-E. Advances in powder diffraction pattern indexing. J. Appl. Crystallogr. 2009, 42, 768−775. (26) Altomare, A.; Caliandro, R.; Camalli, M.; Cuocci, C.; da Silva, I.; Giacovazzo, C.; Moliterni, A. G. G.; Spagna, R. Space-group determination from powder diffraction data: a probabilistic approach. J. Appl. Crystallogr. 2004, 37, 957−966. (27) Altomare, A.; Camalli, M.; Cuocci, C.; Giacovazzo, C.; Moliterni, A. G. G.; Rizzi, R. Advances in space-group determination from powder diffraction data. J. Appl. Crystallogr. 2007, 40, 743−748. (28) Altomare, A.; Camalli, M.; Cuocci, C.; da Silva, I.; Giacovazzo, C.; Moliterni, A. G. G.; Rizzi, R. Space group determination: improvements in EXPO2004. J. Appl. Crystallogr. 2005, 38, 760−767. (29) Le Bail, A.; Duroy, H.; Fourquet, J. L. Ab-initio structure determination of LiSbWO6 by X-ray powder diffraction. Mater. Res. Bull. 1988, 23, 447−452.

in the crystal structure. The melting point was determined to be 462 °C, and sintering temperature for a powder, milled in a planetary mill, was 440 °C. Considering the properties of the PbTeV2O8 phase that have been determined within this study, we can conclude that the material meets a number of very stringent criteria for the ULTCC-I technology, in particular, for capacitor integration. It exhibits an ultralow sintering temperature, chemical compatibility with base electrodes, midpermittivity with relatively low losses, and low temperature coefficient of permittivity. It represents the first material of this kind with the permittivity that allows printing of a capacitor with small size. There could be some environmental concerns due to the presence of Pb; however, in an absence of other alternatives, the presence of Pb is still tolerated like in the case of high-performing piezoelectrics. In addition, on the basis of an analogy with a number of other vanadates,34 it is reasonable to expect that the newly developed cold sintering process can be successfully applied to this material to bring the processing temperatures down toward room temperature. Such processing would make this material compatible with all kinds of different polymer and paper substrates as well as polymer/ceramic composites.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Matjaz Valant: 0000-0003-4842-5676 Jasminka Popović: 0000-0003-0800-2249 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge the financial support from the Slovenian Research Agency (research core funding No. P20377)

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REFERENCES

(1) Sivula, K.; van de Krol, R. Semiconducting Materials for Photoelectrochemical Energy Conversion. Nat. Rev. Mater. 2016, 1, 15010. (2) Abdi, F. F.; Han, L.; Smets, A. H. M.; Zeman, M.; Dam, B.; van de Krol, R. Efficient Solar Water Splitting by Enhanced Charge Separation in a Bismuth Vanadate-Silicon Tandem Photoelectrode. Nat. Commun. 2013, 4, 2195. (3) Khaerudini, D. S.; Guan, G.; Zhang, P.; Hao, X.; Abudula, A. Prospects of Oxide Ionic Conductivity Bismuth Vanadate-Based Solid Electrolytes. Rev. Chem. Eng. 2014, 30, 539−551. (4) Boivin, J. C.; Mairesse, G. Recent Material Developments in Fast Oxide Ion Conductors. Chem. Mater. 1998, 10, 2870−2888. (5) Cheng, F.; Chen, J. Transition Metal Vanadium Oxides and Vanadate Materials for Lithium Batteries. J. Mater. Chem. 2011, 21, 9841−9848. (6) Yu, H.; Liu, J.; Zhang, W.; Zhang, S. Ultra-Low Sintering Temperature Ceramics for LTCC Applications: A Review. J. Mater. Sci.: Mater. Electron. 2015, 26, 9414−9423. (7) Sebastian, M. T.; Wang, H.; Jantunen, H. Low Temperature CoFired Ceramics with Ultra-Low Sintering Temperature: A Review. Curr. Opin. Solid State Mater. Sci. 2016, 20, 151−170. (8) Kähäri, H.; Teirikangas, M.; Juuti, J.; Jantunen, H. Dielectric Properties of Lithium Molybdate Ceramic Fabricated at Room Temperature. J. Am. Ceram. Soc. 2014, 97, 3378−3379. 5667

DOI: 10.1021/acssuschemeng.6b03111 ACS Sustainable Chem. Eng. 2017, 5, 5662−5668

Research Article

ACS Sustainable Chemistry & Engineering (30) Giacovazzo, C. Phasing in Crystallography: A Modern Perspective; IUCr/Oxford University Press: Oxford, England, 2013. (31) Cascarano, G.; Giacovazzo, C.; Camalli, M.; Spagna, R.; Burla, M. C.; Nunzi, A.; Polidori, G. The Method of Representations of Structure Seminvariants. The Strengthening of Triplet Relationships. Acta Crystallogr., Sect. A: Found. Crystallogr. 1984, 40, 278−283. (32) Cascarano, G.; Giacovazzo, C.; Guagliardi, A. Improved figures of merit for direct methods. Acta Crystallogr., Sect. A: Found. Crystallogr. 1992, 48, 859−865. (33) Shannon, R. D. Dielectric polarizabilities of ions in oxides and fluorides. J. Appl. Phys. 1993, 73, 348−366. (34) Baker, A.; Guo, H.; Guo, J.; Randall, C. Utilizing the Cold Sintering Process for Flexible−Printable Electroceramic Device Fabrication. J. Am. Ceram. Soc. 2016, 99, 3202−3204.

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DOI: 10.1021/acssuschemeng.6b03111 ACS Sustainable Chem. Eng. 2017, 5, 5662−5668