Soft-Chemistry Approach To Synthesize Al3+, Ga3+, and Zr4+

Subscriber access provided by GUILFORD COLLEGE

Article

Soft-Chemistry Approach to Synthesize Al3+, Ga3+ and Zr4+ Stabilized Ion-Exchangeable Layered Perovskite Oxides Shalu *, and S. Uma Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.9b00282 • Publication Date (Web): 18 Jul 2019 Downloaded from pubs.acs.org on July 19, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design

Soft-Chemistry Approach to Synthesize Al3+, Ga3+ and Zr4+ Stabilized IonExchangeable Layered Perovskite Oxides Shalu and S. Uma* Materials Chemistry Group, Department of Chemistry, University of Delhi, Delhi 110007, INDIA

ABSTRACT Protonated oxides, H2[Sr2Nb2MO9.5] (M = Al, Ga) and H2[Sr2Nb2ZrO10] related to the Ruddlesden-Popper family of layered perovskite oxides have been successfully synthesised at room temperature starting from Aurivillius phases, Bi2Sr2Nb2MO11.5 (M = Al, Ga) and Bi2Sr2Nb2ZrO12 by the extraction of bismuth oxide sheets using acids. Synthesis of crystalline protonated oxides was also found to be possible under microwave treatment within a short time duration of five minutes. The protonated oxides have been found to undergo facile ionexchange reactions with aqueous solution of NaOH or KOH resulting in novel oxides, A2Sr2Nb2MO9.5 (A = Na, K; M = Al, Ga) and A2Sr2Nb2ZrO10 (A = Na, K), that could not be synthesized by the conventional high temperature solid state synthetic methods. PXRD patterns confirmed the topochemical nature of the reactions by reflecting changes only in the c-dimensions. Rietveld refinements carried out in the case of K+ ion-exchanged products confirm their structural similarity to the Ruddlesden-Popper layered perovskite oxides. The regeneration of the parent bismuth oxides has been possible by the treatment of Na or K layered analogues with BiOCl at 800 °C. The three layer oxygen deficient proton oxides, H2Sr2Nb2MO9.5 (M = Al, Ga) on thermal decomposition yielded cation and anion deficient product oxides possessing ionic conductivities, 2.69×10-2 Scm-1 and 5.86×10-2 Scm-1 at 573 K with activation energies of 0.13 eV and 0.20 eV.

1 ACS Paragon Plus Environment

Crystal Growth & Design 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 34

INTRODUCTION The various members belonging to the family of layered perovskite oxides have gained significance over the years as multifunctional materials and more importantly as basic templates for targeted rational designing of materials similar to the multistep molecular synthesis. The occurrence of the common perovskite sheets, [An-1BnO3n+1] in the Aurivillius oxides, Bi2O2[An-1BnO3n+1], Ruddlesden-Popper oxides, A2'[An-1BnO3n+1] and in the DionJacobson series of oxides, A1'[An-1BnO3n+1] permit the structural transformation within these series of layered perovskites. The two-dimensional perovskite blocks are made up of corner shared BO6 (B = Ti4+, Nb5+, Ta5+) octahedra with varying ‘n’ (thickness of perovskite slab) along with the presence of twelve coordinate A cations (Ca2+, Sr2+, Ba2+, La3+, Bi3+). The perovskite blocks are separated by mobile interlayer A' alkali metal cations in RuddlesdenPopper and Dion-Jacobson series or by [Bi2O2]2+ layers in the Aurivillius series of oxides. Furthermore, these perovskite blocks are robust and thereby interconversions are possible through several topochemical ion exchange, intercalation and metathesis reactions. The topochemical reactions or the soft chemistry methods often include interlayer alkali metal ions exchange by protons (H+) or other univalent ions (

, Ag+) or by different alkali metal

ions (mostly Li+ and Na+ ions) themselves around 300 °C.1-4 Few divalent (Ca2+, Sr2+, Ba2+) and transition metal ions (Co2+, Ni2+, Cu2+, Zn2+) exchange reactions are also possible both in Dion-Jacobson2-4 and in Ruddlesden-Popper series of oxides.5 In addition to these ion exchange reactions, interesting metathesis reactions have been exemplified, thereby providing the opportunity of designing and synthesizing novel intergrowth structures. For example, Wiley et al. have shown the formation of transitionmetal chloride incorporated Dion-Jacobson phase (CuCl) LaNb2O7 through the reaction of RbLaNb2O7 with CuCl2.6 Other transition metal chloride based (MCl)LaNb2O7 (M = V, Cr, Mn, Fe, Co, Cu) intergrowth structures have also been investigated. Similar reactions were 2 ACS Paragon Plus Environment

Page 3 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


possible with other members of Dion-Jacobson series.7 Gopalakrishnan et al. reported the direct conversion of Ruddlesden-Popper phase, K2La2Ti3O10 with BiOCl to form the corresponding Aurivillius oxide Bi2O2[La2Ti3O10].8 This BiOCl reaction was also extended for the n = 1 member of the Ruddlesden-popper phase, NaLaTiO4 resulting in the formation of [BiO][LaTiO4].9 Equally important has been the formation of protonated layered perovskite oxides obtained by Sugahara and co-workers starting from Bi2SrNaNb3O12.10 They reported the extraction of [Bi2O2]2+ sheets with proton incorporation using 6 M HCl at room temperature. This concept has been shown to be successful with other members such as Bi2SrTa2O911 and Bi2CaNaNb3O12.12 The corresponding protonated members retained the layered perovskite framework structures resembling those that were obtained directly by the acid treatment of alkali metal ions containing Ruddlesden-Popper analogues. An effective sequential combination of the above two methods was demonstrated by Mallouk and coworkers2 for the synthesis of H2Sr2Nb2MnO10 starting from the parent Bi2O2[Sr2Nb2MnO10] followed by the subsequent stabilization of Na2Sr2Nb2MnO10. Our interest has been to explore the possibility of converting the modified oxygen-deficient Aurivillius phases into Ruddlesden-Popper phases and to examine the nature of the reverse reactions in order to get back the parent oxides. As a result, it has been possible to achieve the synthesis of anion deficient Ruddlesden-Popper related layered perovskite oxides containing metal ions such as Al3+, Ga3+ and Zr4+ for the first time. Modified Aurivillius intergrowth phases that were assembled using Aurivillius (Bi2Sr2M2'O9) and Brownmillerite (SrM''O2.5) related phases were reported earlier with significant oxygen-ion conductivity. The oxygen deficient Bi2Sr2M2'M''O11.5 (M' = Nb, Ta; M'' = Al, Ga) oxides possess layered structure with tetragonal unit cell (a ~ 3.90 Å; c ~ 33.2 Å) consisting of three-layer oxygen deficient perovskite slabs [Sr2M2'M''O9.5] separated by [Bi2O2]2+ sheets.13 In the present work, we demonstrate the acid extraction of [Bi2O2]2+ sheets using 5 M HCl at room temperature for 72 3 ACS Paragon Plus Environment


Page 4 of 34

h. The protonated oxygen-deficient oxides retained the layering as shown by their powder Xray

diffraction

(PXRD)

patterns

and

were

confirmed

further

using

additional

characterizations including thermogravimetric (TG) analysis and field emission scanning electron microscopy (FESEM). In addition, we have carried out the ion-exchange reactions to obtain the respective alkali metal (Na+, K+) based layered oxides. The reactions of (Na+, K+) exchanged oxides with BiOCl at 800 °C resulted in the formation of the starting Aurivillius related precursor phases. The reactivity of the protonated oxides towards their ability to intercalate organic amine has also been probed. Finally, the thermal decomposition studies of the proton containing oxides giving rise to oxides with cation and anion deficiencies are also presented. EXPERIMENTAL SECTION Synthesis of Bi2Sr2Nb2MO11.5 (M = Al, Ga) and Bi2Sr2Nb2ZrO12 Samples of Bi2Sr2Nb2AlO11.5 (BSNA) and Bi2Sr2Nb2GaO11.5 (BSNG) were prepared through the solid state synthesis precursor method using the reactants Nb2O5 (Sigma Aldrich, 99.9%), Bi2O3 (Sigma Aldrich, 99.9%), Al2O3 (Central Drug House, 99%), Ga2O3 (Sigma Aldrich, 99.99%), ZrO(NO3)2.xH2O (SRL, 99.5 %) and SrCO3 (Sigma Aldrich, 98%). A stoichiometric precursor excluding bismuth oxide was obtained initially after homogenizing and heating at 800 °C and at 900 °C for 12h. The resulting precursors containing aluminium and gallium were independently mixed with requisite amounts of Bi2O3 to produce BSNA and BSNG oxides by heating at 800 °C for 12 h and at 870 °C for 12 h. This method also minimized significantly the amount of β-Bi2O3 phase obtained along with the formation of BSNG.14 Polycrystalline Bi2Sr2Nb2ZrO12 (BSNZ) was synthesized by adopting a similar precursor method and experimental conditions. Synthesis of layered perovskite derivatives


Page 5 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Room temperature acid extraction of [Bi2O2]2+ sheets were best achieved by stirring 1 g of polycrystalline samples of BSNA, BSNG and BSNZ with 200 cm3 of 5 M (mol dm-3) HCl for 72 h. Additionally, 2 g of the parent oxides were taken with 100 mL of 5 M HCl to perform the microwave assisted reactions using a domestic microwave (Samsung, Model no. CE76JD/XTL). Microwave reactions were always limited for duration of 5 minutes. The acid treated products were washed with deionised water, then filtered and dried at room temperature. The acid-treated products after characterization were adopted for the further alkali ion-exchange (Na+, K+) reactions. For Na+ or K+ exchange reactions, 0.5 g of proton compound was treated with 0.5 M NaOH or 1 M KOH following the same synthetic approach as discussed above. In case of amine intercalation reactions, 0.5 g of HSNA/HSNG was refluxed with 50 mL solution of n-octylamine (50 mass %) in hexane. Mostly Na+-exchanged layered derivatives were treated with BiOCl at 800 °C temperature in air to derive back the parent members. CHARACTERIZATION The PXRD patterns of all the samples were collected with a high resolution X’Pert PANanalytical diffractometer equipped with Xe proportional detector employing Cu Kα radiation (λ = 1.5418 Å) over the range of 3-70° at 25 °C. To carry out Rietveld refinements data were collected over the range 3-100° with a scan width of 0.04° and a scan rate of 4.3 s per step at 25 °C. Le Bail refinements of lattice parameters and Rietveld refinements were performed using TOPAS 315 and GSAS + EXPGUI program.16, 17 TG analysis of acid-treated and alkali exchanged products were performed using NETZSCH STA-449 F3 instrument in the temperature range of 30-700 °C at a heating rate of 10 °C/min. The elemental quantitative analysis of as prepared samples was determined from inductively coupled plasma emission spectroscopy (ICP) measurements employing for Vista MPX varian ICP-AES. FESEM micrographs of the samples were carried out using Hitachi S-3700 M and JEOL6610LV 5 ACS Paragon Plus Environment


Page 6 of 34

microscope. Elemental analysis of the amine intercalated samples was carried out using an Elementar Analysenysteme GMBH Varion EL III by the combustion method. The AC conductivity measurement were performed on sintered (at 623 K) pellets (with diameter of 13 mm and thickness of 1.39 mm) sputtered on both sides with silver electrodes using a Novocontrol α-S high-resolution broad band dielectric analyzer in a frequency range from 0.1 Hz to 1.0 MHz with an oscillation voltage of 0.5 V under nitrogen atmosphere (Alpha N analyzer Novocontrol, Pt electrode). Additionally, conductivity isotherms were also measured in oxygen partial pressures (pO2) of 1 atm using a mass flow controller (MFC) (D08-1FM series, seven star) with an accuracy of ±1 sccm. The conductivity isotherms were collected in the temperature range 313-573 K. RESULTS AND DISCUSSION Synthesis and acid treatment of BSNA and BSNG The parent bismuth containing oxides were synthesized by using the precursor route without involving the extended heat treatment at elevated temperatures (˃ 1000 °C).13 The PXRD patterns for the polycrystalline samples of BSNA and BSNG by profile matching using the Le Bail method resulted in the tetragonal cell parameters, a = 3.9054 (2) Å; c = 33.244 (3) Å and a = 3.9066 (2) Å; c = 33.247 (2) Å (S.G. P4/mmm) respectively (Figure 1, Table 1). Trial experiments involving the usage of acids of concentrations 2 M, 3 M and 4 M HCl at room temperature (30 °C) did not result in complete extraction of bismuth. The PXRD pattern of HSNA obtained after the acid treatment using 5 M HCl through stirring, followed by drying at 30 °C, displayed specific low angle (00l) reflections, substantiating the phase transformation of the Aurivillius oxide (Figure 2a). The appearance of the broader mixed (hkl) reflections indicates a possible stacking disorder in the layered structure.10 Similar observations were noticed for the Ga containing BSNG oxide (Figure 2b). The usage of microwave radiation assisted methods for the various transformations and functionalization 6 ACS Paragon Plus Environment

Page 7 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of layered perovskites is gaining momentum.18-21 These methods significantly reduce the reaction time to produce products in greater yield as compared to the conventional experimental methods of heating. The acid extraction of BSNA and BSNG oxides assisted by microwave process have been found to be convenient as shown by the production of crystalline products within ~5 minutes (Figure 2c and 2d). All the reflections in the PXRD patterns of the acid-treated products (HSNA and HSNG) dried at room temperature (30 °C) can readily be indexed in a tetragonal symmetry. However, unlike their parent bismuth based oxides, the indexation can be achieved even with half of the c-axis (~15.55 Å). The presence of (100) reflection (2θ~22.8°) coincides with the primitive tetragonal symmetry (S.G. P4/mmm) instead of the alternate body-centred tetragonal symmetry (S.G. I4/mmm). The refined lattice parameter using a profile match are a = 3.8994 (2) Å and c = 15.754 (4) Å for HSNA and a = 3.9016 (2) Å and c = 15.802 (2) Å for HSNG (Table 1). The structural characteristics of the oxides, specially the protonated layered perovskites depend upon the intercalation of water molecules in the interlayer space. Accumulation of water in the galleries of the interlayer region has been a common phenomenon occurring in many of the parent alkali metal (Na+, K+) ion oxides and their protonated derivatives belonging to the Dion-Jacobson and Ruddlesden-Popper type structural families.22 Similarly, the proton compounds obtained by leaching of [Bi2O2]2+ sheets led to the formation of hydrate, (H1.8[Bi0.2Sr0.8NaNb3O10].0.4H2O) as deduced from the TG studies of the room temperature dried samples. The corresponding anhydrous product was obtained by drying at 120 °C.10 TG plots recorded for the protonated, H2[Sr2Nb2MnO10] resulted in a total weight loss of 6.5% and 3.1% respectively for the samples dried at 30 °C and at 120 °C. The higher weight loss noted for the room temperature dried sample included the loss due to the intercalated (1.35) water molecules in the range 50-130 °C.23 The verification by TG analysis of HSNA and HSNG samples dried at 30 °C exhibited a weight loss beginning at 40 °C and 7 ACS Paragon Plus Environment


Page 8 of 34

resulted in a total loss of 4.5% and 4.6% respectively (Figure 3a). TG curves of HSNA and HSNG oxides dried at 120 °C displayed a reduction in the weight loss (2.8% and 3%) (Figure 3b). The observed results from TG experiments are in agreement with 0.5 (HSNA) and 0.6 (HSNG) water molecules present either in the interlayer or adsorbed on the surface. The PXRD patterns of the hydrates show a systematic increase of ~1.5 Å (HSNA and HSNG) in the c-parameters indicating the introduction of interlayer water molecules (Figure 2, Table 1). The extraction of [Bi2O2]2+ sheets results in a structure neither with the doubling of c-axis nor a change in the lattice type (P to I or vice versa). The lattice dimensions of the protonated oxides only are associated with a reduction in the c parameter values, when compared with (c/2) value of the parent oxides, coinciding with the removal of [Bi2O2]2+ sheets from the structures. These observations can be summarized to conclude the presence of an average structure without actually including the stacking sequence of the adjacent perovskite slabs.12 The comparison of FESEM images of the parent BSNA and BSNG oxides and that of the protonated HSNA and HSNG oxides confirm the preservation of the well-defined rod and plate like morphologies (Figure 4). Additionally, ICP analyses of the products were carried out to determine their compositions. The ratio of Bi and Sr is 0.2 to 0.8, while quantities of Al and Nb do not show any variation beyond the experimental standard deviations. The cation disorder leading to the exchange of 0.2 Sr2+ into the Bi-O sheets and the presence of 0.2 of Bi3+ in Sr2+ sites of the perovskite blocks is known to be a common occurrence in the parent Aurivillius oxides11. For simplicity, the samples are continued to be referred as HSNA (H2[Sr2Nb2AlO9.5]) and HSNG (H2[Sr2Nb2GaO9.5]) while explaining their topochemical reactions further. On the whole, the stabilization of HSNA and HSNG oxides with structural features intact, in spite of the oxygen deficiency opens up further possibilities of attaining novel layered perovskite materials by adopting this synthetic approach. Topochemical reactions of HSNA and HSNG 8 ACS Paragon Plus Environment

Page 9 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The ion-exchange reactions of the acid compounds, HSNA with aqueous solutions of NaOH and KOH lead to the formation of new layered perovskite oxides, (Na2[Sr2Nb2AlO9.5] (NSNA) and K2[Sr2Nb2AlO9.5] (KSNA)) related to Ruddlesden-Popper structures (Figure 5). The novelty in the present study has been the possibility of exchange reactions merely by stirring around 40-50 °C or simply by treating the reactants under microwave radiation for few (~5) minutes (Figure S1, Supporting Information). Similar ion-exchange reactions of HSNG with NaOH and KOH solutions yielded respectively Na2[Sr2Nb2GaO9.5] (NSNG) and K2[Sr2Nb2GaO9.5] (KSNG). Particularly, the low angle (00l) reflections seen in the PXRD patterns of the Na+ and K+ containing members confirm the preservation of the layered structures (Figure S2, Supporting Information). The FESEM images of the ion-exchanged products show the formation of rectangular along with irregular agglomerated crystallites (Figure S3, Supporting Information). The formation of hydrates along with the estimate of the water molecules ~1.4 and ~3.2 respectively for NSNA and KSNA were verified from the respective TG curves (Figure S4, Supporting Information). PXRD patterns of the hydrates, Na2Sr2Nb2AlO9.5.1.42H2O and K2Sr2Nb2AlO9.5.3.19H2O were distinctly different (Figure 5). A comparative Le Bail profile fitting confirmed that complete indexation of the former was feasible only by using a c-parameter of ~ 33.5 Å (S.G. (I4/mmm), while that of the hydrated KSNA required a c-parameter of ~ 16 Å in (S.G. P4/mmm) (Figure S5, Supporting Information). The doubling of the c-parameter caused usually by the displacement of (a+b)/2 in order to accommodate the smaller Na+ ions and the water molecules. The anhydrous oxide obtained by drying at 120 °C for NSNA reversed back to a unit cell without the doubling of the c-parameter (~ 15 Å; S.G. P4/mmm), but with a decrease of ~ 2 Å owing to the removal of the water molecules and for the anhydrous KSNA only a decrease in the c parameter (~ 3 Å) corresponding to the removal of the interlayer water molecules has been observed (Table 1, Figure S1, Supporting Information). The analogous gallium containing Na+ exchanged 9 ACS Paragon Plus Environment


Page 10 of 34

(NSNG) and K+ exchanged (KSNG) products exhibited the aforementioned structural difference between the hydrate and anhydrous forms (Table 1). A difference of ~2.1 Å in the c-parameter has been realized from the analysis of the PXRD measurements that corroborated with the TGA results obtained for the hydrates Na2Sr2Nb2GaO9.5.1.45H2O and K2Sr2Nb2GaO9.5.3.19H2O (Figure S2 and S4, Supporting Information). The preservation of the layered structure over the sequence of reactions starting from the parent bismuth oxides to that of the protonated oxides followed by alkali metal (Na+, K+) ions exchange is evident from the PXRD measurements and the derived lattice parameters. We attempted to carry out Rietveld refinements for one of the ion-exchanged compounds in order to verify the amount of incorporated interlayer ions and to determine any variation if present in the proportion of ions present in the perovskite blocks. Although, the PXRD patterns of the protonated and Na+/K+ exchanged products suggested the structures to be similar to those of the Ruddlesden-Popper layered phases, additional complexity exists because of the unavailability of suitable structural models in appropriate space groups. Furthermore, anionic deficiency has also been introduced during the conversion of the modified Aurivillius phases to the protonated and subsequently to the other ion-exchanged products. Rietveld refinement trials were performed for the hydrated KSNA using the structural model of K2La2Ti3O10.2H2O (S.G. P4/mmm; a = b = 3.8585 Å, c = 16.814 Å) (Figure 6). The refinement converged after considering (i) a decrease in the interlayer ions (K+); (ii) presence of smaller amount (~ 0.14) of Bi3+ along with Sr2+ ions within the perovskite blocks and lastly (iii) the oxygen vacancies as compared to the known K2La2Ti3O10.2H2O. The refinement results are summarized in Tables S1 and S2, supporting information. The refined composition (K1.277(2)Sr1.668(8)Bi0.133(6)Nb2AlO9.115(6).2.35H2O), confirms the presence of the three octahedral thickness layered perovskite blocks, even though it differs marginally from the expected stoichiometry in terms of the interlayer K+, Sr2+ ions and water molecules. 10 ACS Paragon Plus Environment

Page 11 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Finally, it is possible to reintroduce the [Bi2O2]2+ sheets through the reactions between Na2[Sr2Nb2MO9.5] (M = Al, Ga) and K2[Sr2Nb2MO9.5] (M = Al, Ga) oxides with stoichiometric amounts of BiOCl at 800 °C. The PXRD patterns of the dried products after washing the by-products (NaCl/KCl), with distilled water matched well with the starting modified Aurivillius members, Bi2O2[Sr2Nb2MO9.5] (M = Al, Ga) (Figure 7a). A small amount of β-Bi2O3 impurity in the PXRD patterns of the regenerated parent oxides appear due to the cation-disorder between the Bi3+ ions in (Bi2O2)2+ sheets and Sr2+ ions in the perovskite blocks as mentioned earlier, during the formation of the protonated oxides. The overall reactions involved in the production of new ion-exchangeable layered perovskite oxides followed by the final regeneration step are shown schematically (Scheme 1). The regenerated oxide (BSNA) was also found to be capable of undergoing another cycle of reactions depicted in the scheme confirming the usefulness of the low temperature reactions (Figure 7b). Protonated forms of layered perovskites made up of perovskite slabs of lower charge (≤ 1), such as the members of Dion-Jacobson series undergo routine amine intercalation reactions. Protonated members of Ruddlesden-Popper phases possessing a charge of two, have been known to intercalate amines only after exfoliation into single sheets using polymeric surfactants.24 However, protonated members related to the Ruddlesden-Popper series synthesized in a manner as discussed in the present work, undergo facile intercalation reaction with linear n-alkylamines. The reactions of HSNA and HSNG with n-octylamine using n-hexane as solvent resulted in amine intercalated products. Chemical analysis of the amine intercalated products of HSNA and HSNG [C, 16.02 mass %; H, 3.52 mass %; N, 1.91 mass %] and [C, 14.89 mass %; H, 3.38 mass %; N, 1.97 mass %] were in agreement to the intercalation of 1.0 mole of amine. The increase in the interlayer spacing as shown by the typical low angle (00l) reflections in the PXRD patterns are consistent with the incorporation 11 ACS Paragon Plus Environment


Page 12 of 34

of amines most likely in a bilayer arrangement within the interlayer region (Figure 8). The aparameter does not vary, while the difference in the c/2 parameter with that of c-parameter of the protonated oxide (~1.5 Å) matches with the earlier n-octylamine intercalated data (Table 1).12,25 Topochemical condensation reactions with the removal of oxygen yielding novel three dimensional perovskites have been one of the most significant property of the protonated layered perovskite oxides. Several examples leading to the creation of metastable solids have been achieved simply by heating above 300 °C.2 Specially, A-site vacant oxides such as La2/3TiO3,

CaNaTa3O9,

Ca2Ti2O9

and

SrLaTi2TaO9

starting

from

H2La2Ti3O10,

H2CaNaTa3O10, H2Ca2Ta2TiO10 and H2SrLaTi2TaO10 are produced by respective topochemical dehydration reactions. In the present study, because of the oxygen deficient nature of the proto compounds, HSNA and HSNG, their dehydration at 350 °C, resulted in vacancies at the A-site (cation) along with oxygen (anion) deficiency (Figure 9). The PXRD patterns of the products, □Sr2Nb2AlO8.5 and □Sr2Nb2GaO8.5 are indexed using primitive tetragonal unit cell parameters (a = 3.925 (5)Å; c = 14.26 (5)Å and a = 3.928 (6) Å; c = 14.38 (5)Å).26 The ionic conductivity measurements under an atmosphere of nitrogen indicate moderate conductivity for HSNA (3.37×10-7 Scm-1) and HSNG (1.05×10-7 Scm-1) at 573K (Figure 9(iii)). The corresponding activation energies are 0.71 eV and 0.60 eV. The conductivity measurements under oxygen atmosphere showed higher conductivity values for HSNA (2.69×10-2 Scm-1) and HSNG (5.86×10-2 Scm-1) with lower activation energies (0.13 eV and 0.20 eV) (Figure 9(iii) (Inset)). The increase in the conductivity values in the oxygen atmosphere confirm the higher concentration oxygen vacancies in the lattice and the approach can be utilized for the production of efficient solid electrolytes. Interlayer chemistry of zirconium based layered perovskite oxides


Page 13 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Acid extraction of [Bi2O2]2+ sheets to produce ion-exchangeable protonated layered compounds has proved to be further useful to introduce Zr4+ for the first time in the layered perovskites. Unlike Ti4+ or Nb5+, Zr4+ has not been stabilized so far by the high temperature solid state synthesis neither in the Dion-Jacobson series nor in the Ruddlesden-Popper series of layered oxides. The incorporation of Zr in the Aurivillius oxide (Bi2Sr2Nb2ZrO12) provided the perfect opportunity to exploit the various ion-exchange processes in order to synthesize Ruddlesden-Popper based zirconium containing layered perovskite oxide. The PXRD pattern of Bi2Sr2Nb2ZrO12 (BSNZ) matched with the PXRD pattern reported earlier (Figure 10).27 Refined tetragonal lattice parameters (S.G. P4/mmm) are listed in Table 1. It is possible to synthesize the proton incorporated H1.8[Bi0.2Sr0.8Nb2ZrO10] (HSNZ) oxide through roomtemperature treatment or under microwave radiation by treating the BSNZ oxide with 5M HCl. All the reflections in the PXRD pattern are successfully accounted for using a primitive tetragonal cell with a reduction in the c-parameter in accordance with the removal of [Bi2O2]2+sheets (Figure 10). The room temperature dried HSNZ showed continuous loss of intercalated water (~ 0.68) as well the loss of one molecule of water arising from the proton content of 1.8-2.0 (Figure S6, Supporting Information). The acid form of the layered oxide is capable of undergoing ion-exchange reactions to form the Na+ or K+ analogues with solutions of NaOH or KOH under microwave assisted conditions (Figure 10). The PXRD patterns exhibit appropriate shift in the 2θ values particularly for the c-dependent reflections (Table 1). Finally, it has been also possible to complete the overall cyclic process regenerating the parent BSNZ oxide by heating the NSNZ with BiOCl at 800˚C. CONCLUSION We have utilized the approach of inserting protons through acid leaching of [Bi2O2]2+ sheets from the Aurivillius phases to achieve the target of Al3+, Ga3+ and Zr4+ incorporated layered oxides. The selective leaching of Aurivillius phases can be completed by room temperature 13 ACS Paragon Plus Environment


Page 14 of 34

stirring over a period of three days and it has been possible to fasten the products formation under microwave conditions. The protonated oxides, H2[Sr2Nb2MO9.5] (M = Al, Ga) behave as typical Bronsted acids as shown by their reactions with organic bases to form amine intercalated products and further capable of reacting with aqueous solutions of inorganic bases such as NaOH or KOH to form the respective sodium and potassium exchanged products. PXRD patterns and Rietveld refinements of the K+ exchanged oxide confirm the topochemical nature of the reactions. Further, the reaction of the layered perovskites phases with BiOCl promptly resulted in the regeneration of the parent Aurivillius phases. Thermal decompositions of the proton oxides directed the topochemical condensation reaction to yield the respective cation and anion deficient perovskites with appreciable oxide ion conductivities (~ 10-2 Scm-1 at 573 K). We have additionally shown that a novel Zr4+ substituted layered perovskite oxide formation is possible by executing the reactions starting from Bi2Sr2Nb2ZrO12. For the first time, ion-exchangeable Zr4+ substituted layered perovskite related to Ruddlesden-Popper phase has been produced by carrying out a sequence of topochemical reactions. The results point out to the potential available behind the softchemistry based reactions of layered perovskites to yield entirely new oxides that are otherwise inaccessible under normal thermodynamic conditions. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Le Bail refinements of NSNA, KSNA, NSNG and KSNG, TG data and FESEM images. AUTHOR INFORMATION Corresponding author *E-mail: [email protected] ORCID: 14 ACS Paragon Plus Environment

Page 15 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Sitharaman Uma:0000-0001-7448-2936 Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS Authors thank DST-SERB (EMR/2016/006762), DST-SERB (EMR/2016/006131), Govt of India and DU-DST PURSE Grant for financial support to carry out this work. Shalu thanks UGC for JRF fellowship. REFERENCES [1] Gopalakrishnan, J. Chimie Douce Approaches to the Synthesis of Metastable Oxide Materials. Chem. Mater. 1995, 7, 1265-1275. [2] Schaak, R. E.; Mallouk, T. E. Perovskites by Design: A Toolbox of Solid-State Reactions. Chem. Mater. 2002, 14, 1455-1471. [3] Ranmohotti, K. G. S.; Josepha, E.; Choi, J.; Zhang, J.; Wiley, J. B. Topochemical Manipulation of Perovskites: Low-Temperature Reaction Strategies for Directing Structure and Properties. Adv. Mater. 2011, 23, 442-460. [4] Uma, S. In Handbook of Solid State Chemistry; Dronskowski, R., Kikkawa, S., Stein, A., Eds.; Wiley-VCH: Weinheim, Germany, 1st edition, 2017; Chapter 15, pp 571-594. [5] Hyeon, K.-A.; Byeon, S.-H. Synthesis and Structure of New Layered Oxides, MIILa2Ti3O10 (M) Co, Cu, and Zn. Chem. Mater. 1999, 11, 352-357. [6] Kodenkandath, T. A.; Lalena, J. N.; Zhou, W. L.; Carpenter, E. E.; Sangregorio, C.; Falster, A. U.; Simmons, W. B.; O’ Connor, C. J.; Wiley, J. B. Assembly of Metal-Anion Arrays within a Perovskite Host. Low-Temperature Synthesis of New Layered CopperOxyhalides, (CuX)LaNb2O7, X = Cl, Br. J. Am. Chem. Soc. 1999, 121, 10743-10746. [7] Viciu, L.; Caruntu, G.; Royant, N.; Koenig, J.; Zhou, W.L.; Kodenkandath T. A.; Wiley, J. B. Formation of Metal-Anion Arrays within Layered Perovskite Hosts. Preparation of a 15 ACS Paragon Plus Environment


Page 16 of 34

Series of New Metastable Transition-Metal Oxyhalides, (MCl)LaNb2O7 (M = Cr, Mn, Fe, Co). Inog. Chem. 2002, 41, 3385-3388. [8] Gopalakrishnan, J.; Sivakumar, T.; Ramesha, K.; Thangadurai, V.; Subbanna, G. N. Transformations of Ruddlesden-Popper Oxides to New Layered Perovskite Oxides by Metathesis Reactions. J. Am. Chem. Soc. 2000, 122, 6237-6241. [9] Sivakumar, T.; Seshadri, R.; Gopalakrishnan, J. Bridging the Ruddlesden-Popper and the Aurivillius Phases: Synthesis and Structure of a Novel Series of Layered Perovskite Oxides, (BiO)LnTiO4 (Ln = La, Nd, Sm). J. Am. Chem. Soc. 2001, 123, 11496-11497. [10] Sugimoto, W.; Shirata, M.; Kuroda, K.; Sugahara, Y. New Conversion Reaction of an Aurivillius Phase into the Protonated Form of the Layered Perovskite by the Selective Leaching of the Bismuth Oxide Sheet. J. Am. Chem. Soc. 1999, 121, 11601-11602. [11] Tsunoda, Y.; Shirata, M.; Sugimoto, W.; Liu, Z.; Terasaki, O.; Kuroda K.; Sugahara, Y. Preparation and HREM Characterization of a Protonated Form of a Layered Perovskite Tantalate from an Aurivillius Phase Bi2SrTa2O9 via Acid Treatment. Inorg. Chem. 2001, 40, 5768-5771. [12] Sugimoto, W.; Shirata, M.; Kuroda K.; Sugahara, Y. Conversion of Aurivillius Phases Bi2ANaNb3O12 (A = Sr or Ca) into the Protonated Forms of Layered Perovskite via Acid Treatment. Chem. Mater. 2002, 14, 2946-2952. [13] Kendall, K. R.; Thomas, J. K.; Loye, H.-C. Z. Synthesis and Ionic Conductivity of a New Series of Modified Aurivillius Phases. Chem. Mater. 1995, 7, 50-57. [14] Speakman, S. A.; Haluska, M. S.; Say, C. A.; Misture, S. T. A Reappraisal of Fast Ion Conduction in Ta, Ga, and Al-Substituted Aurivillius Phases. Solid State Ionics 2005, 176, 2617-2623. [15] Coelho, A. A. TOPAS User Manual, version 3.1; Bruker AXS GmbH: Karlsruhe, Germany, 2003; pp 1-68. 16 ACS Paragon Plus Environment

Page 17 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[16] A. C. Larson, R. B. Von Dreele, General Structure Analysis System (GSAS); Los Alamos National Laboratory Report LAUR 86-748; Los Alamos National Laboratory: Los Alamos, NM, 2004. [17] B. H. Toby, J. Appl. Crystallogr., 2001, 34, 210-213. [18] Boykin, J. R.; Smith, L. J. Rapid Microwave-Assisted Grafting of Layered Perovskites with n‑Alcohols. Inorg. Chem. 2015, 54, 4177-4179. [19] Wang, Y. Delahaye, E.; Leuvrey, C.; Leroux, F.; Rabu, P.; Rogez, G. Efficient Microwave-Assisted Functionalization of the Aurivillius-Phase Bi2SrTa2O9. Inorg. Chem. 2016, 55, 4039-4046. [20] Wang, Y.; Delahaye, E.; Leuvrey, C.; Leroux, F.; Rabu, P.; Rogez, G. Post-Synthesis Modification of the Aurivillius Phase Bi2SrTa2O9 via in Situ Microwave-Assisted “Click Reaction”. Inorg. Chem. 2016, 55, 9790-9797. [21] Akbarian-Tefaghi, S.; Wiley J. B. Microwave-Assisted Routes for Rapid and Efficient Modification of Layered Perovskites. Dalton Trans. 2018, 47, 2917-2924. [22] Schaak, R. E.; Mallouk, T. E. A2Ln2Ti3010 (A = K or Rb; Ln = La or Rare Earth): A New Series of Layered Perovskites Exhibiting Ion Exchange. Chem. Mater. 2000, 12, 3427-3434. [23] Bi2Sr2Nb2MnO12 (1 g) was stirred with 5 M HCl (200 ml) at 30 °C for a period of 3 days. The resulting product after washing and drying at 30 °C depicted weight loss of 6.5% in the TG experiments. While the product dried at 120 °C, showed a reduced weight loss of 3.1%, confirming water of hydration to be 1.35 H2O. The tetragonal lattice parameters for the hydrated proton compounds are (a = 3.8856 (2) Å; c = 31.523 (3) Å) and for the anhydrous are (a = 3.8965 (4) Å; c = 29.495 (3) Å). [24] Schaak, R. E.; Mallouk, T. E. Prying Apart Ruddlesden-Popper Phases: Exfoliation into Sheets and Nanotubes for Assembly of Perovskite Thin Films. Chem. Mater. 2000, 12, 34273434. 17 ACS Paragon Plus Environment


Page 18 of 34

[25] Jacobson, A. J.; Johnson, J. W.; Lewandowski, J. T. Interlayer Chemistry between Thick Transition-Metal Oxide Layers: Synthesis and Intercalation Reactions of K[Ca2Nan3NbnO3n+l]

(3 ≤ n ≤ 7). Inorg. Chem. 1985, 24, 3727-3729.

[26] Bhuvanesh, N. S. P.; Crosnier-Lopez, M. -P., Duroyb, H.; Fourquet, J. -L. Synthesis, Characterization and Dehydration Study of H2A0.5nBnO3n+1.xH2O (n = 2 and 3, A = Ca, Sr and B=Nb, Ta) Compounds Obtained by Ion-Exchange from the Layered Li2A0.5nBnO3n+1 perovskite materials. J. Mater. Chem. 2000, 10, 1685-1692. [27] Mandal, T. K.; Sivakumar, T.; Augustine, S.; Gopalakrishnan, J. Heterovalent CationSubstituted Aurivillius Phases, Bi2SrNaNb2TaO12 and Bi2Sr2Nb3-xMxO12 (M = Zr, Hf, Fe, Zn). Mater. Sci. Eng. B 2005, 121, 112-119.


Page 19 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


FIGURE CAPTIONS Figure 1 Le Bail refinement of PXRD patterns of polycrystalline samples (a) BSNA and (b) BSNG (blue line, experimental data; pink line; calculated profile; green line below, difference profile; vertical bars, Bragg positions). Figure 2 Le Bail refinements of PXRD patterns for hydrated and anhydrous protonated oxides obtained at room temperature by the acid extraction of (a) BSNA and (b) BSNG (blue line, experimental data; pink line; calculated profile; green line below, difference profile; vertical bars, Bragg positions). Respective PXRD patterns for the product obtained through microwave assisted process are shown in (c) and (d). Figure 3 TG curves of samples obtained by acid extraction of BSNA and BSNG dried (a) at room temperature and (b) at 120 °C. Figure 4 FESEM images of polycrystalline sample of (a) BSNA and its (b) proton compound obtained by acid treatment at room temperature, (c) BSNG and its (d) protonated compound obtained by acid treatment at room temperature. Figure 5 PXRD patterns of the ion-exchanged products of HSNA (hydrate) with (a) NaOH and (b) KOH solutions. Figure 6 Rietveld refinement for the PXRD pattern of the ion-exchanged product of HSNA (hydrate) with KOH solution (red line, experimental data; green line; calculated profile; pink line below, difference profile; vertical bars, Bragg positions). Figure 7 (a) Le Bail refinements of PXRD patterns of regenerated BSNA and BSNG, obtained by the treatment of alkali exchanged samples with BiOCl (blue line, experimental data; pink line; calculated profile; green line below, difference profile; vertical bars, Bragg positions). (b) PXRD patterns of the regenerated (i) BSNA, (ii) its protonated compound and (iii) the ion-exchanged of proton compound using NaOH solution. Inset shows the expanded



Page 20 of 34

2θ range (24-28°) for the PXRD pattern of the regenerated BSNA. (“*” shows reflections arising from β-Bi2O3). Figure 8 (a) PXRD patterns and their respective (b) Le Bail refinement of amine intercalated products of (i) HSNA and (ii) HSNG (blue line, experimental data; pink line; calculated profile; green line below, difference profile; vertical bars, Bragg positions). Figure 9 (i) PXRD patterns and (ii) Le Bail refinements for the products obtained after thermal decomposition (350˚C) of the protonated samples of (a) HSNA and (b) HSNG (blue line, experimental data; pink line; calculated profile; green line below, difference profile; vertical bars, Bragg positions). The corresponding Arrhenius plots for the dc conductivity measurements in oxygen and nitrogen (inset) atmosphere are shown. The symbols represent experimental data points, while the solid lines correspond to the linear fitting. Figure 10 PXRD patterns of (i) BSNZ, (ii) HSNZ, (iii) NSNZ and (iv) product obtained after reaction of NSNZ with BiOCl (“*” shows reflection corresponding to β-Bi2O3).


Page 21 of 34


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

(b)

Figure 1



Anhydrous

(a)

Hydrate

Anhydrous

(b)

Hydrate

Hydrate

Anhydrous

Page 22 of 34

(c)

Anhydrous

(d)

Hydrate

Figure 2


Page 23 of 34


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3



Page 24 of 34

Figure 4


Page 25 of 34


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 5



Page 26 of 34

Figure 6


Page 27 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a) BSNG

*

BSNA

(b)

Figure 7



Page 28 of 34

(a)

(ii)

(i)

(b) (ii)

(i)

Figure 8


Page 29 of 34


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 9



Page 30 of 34

2θ (degree)

Figure 10


Page 31 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1 Lattice parameters of the Aurivillius phases and the products obtained by various topochemical reactions. Chemical composition

a/(Å)

c/(Å)

Space group

BSNA

3.9054 (2)

33.244 (3)

P4/mmm

HSNA‡

3.8994 (2)

15.754 (4)

P4/mmm

HSNA

3.9102 (3)

14.235 (2)

P4/mmm

NSNA‡

3.9066 (2)

33.692 (2)

I4/mmm

NSNA

3.9212 (3)

14.848 (3)

P4/mmm

KSNA‡

3.9114 (1)

16.827 (1)

P4/mmm

KSNA

3.9249 (3)

14.642 (5)

P4/mmm

BSNG

3.9066 (2)

33.247 (2)

P4/mmm

HSNG‡

3.9016 (2)

15.802 (2)

P4/mmm

HSNG

3.9125 (5)

14.321 (4)

P4/mmm

NSNG‡

3.9148 (5)

33.579 (2)

I4/mmm

NSNG

3.9260 (3)

14.695 (2)

P4/mmm

KSNG‡

3.9286 (4)

16.861 (3)

P4/mmm

KSNG

3.9254 (1)

14.458 (4)

P4/mmm

BSNZ

3.9214 (2)†

33.581 (3)

P4/mmm

HSNZ‡

3.9093 (3)

30.685 (2)

P4/mmm

HSNZ

3.9046 (5)

27.912 (2)

P4/mmm

NSNZ‡

3.9245 (3)

33.402 (1)

I4/mmm

KSNZ‡

3.9242 (3)

33.442 (3)

P4/mmm

C8A-HSNA

3.9102 (3)

34.531 (3)

P4/mmm

C8A-HSNG

3.9109 (4)

34.532 (8)

P4/mmm

‡ hydrates † a-parameter is not doubled for uniformity.



Page 32 of 34

Scheme 1 Representation of the conversion of the oxygen deficient Aurivillius phases Bi2Sr2Nb2MO11.5 (M = Al or Ga) to the corresponding ion exchanged (H+, Na+, K+) and amine intercalated oxygen deficient layered perovskite phases, along with the regeneration of the parent oxides.


Page 33 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


“For Table of Contents Use Only”

Soft-Chemistry Approach to Synthesize Al3+, Ga3+ and Zr4+ Stabilized IonExchangeable Layered Perovskite Oxides

Shalu and S. Uma* Materials Chemistry Group, Department of Chemistry, University of Delhi, Delhi 110007, INDIA

Design and generation of ion-exchangeable layered perovskite oxides through topochemical reactions



Design and generation of ion- exchangeable layered perovskite oxides through topochemical reactions 254x190mm (96 x 96 DPI)

ACS Paragon Plus Environment

Page 34 of 34

Soft-Chemistry Approach To Synthesize Al3+, Ga3+, and Zr4+

Recommend Documents