A Comparison of Order-Disorder in Several Families of Cubic Oxides

Abstract

Order-disorder on both cation and oxygen sites is a hallmark of fluorite-derived structures, including pyrochlores. Ordering can occur on long- and short-range scales and can result in persistent metastable states. In various cubic oxide systems, different types of disorder are seen. The purpose of this paper is to review and compare the types and energetics of order-disorder phenomena in several families of cubic oxides having pyrochlore, weberite, defect fluorite, perovskite, rocksalt, and spinel structures. The goal is to better understand how structure, composition, and thermodynamic parameters (enthalpy and entropy) determine the feasibility of different competing ordering processes and structures in these diverse systems.

Refined structural studies on the fluorite-related polymorphs of sol–gel undoped and Eu3+-doped yttrium tantalates

“…31 In this structure, Y 3+ and Ta 5+ randomly occupy the same symmetry site (4a Wyckoff position) at a 3 : 1 ratio; 24,32,48 one oxygen vacancy is created per unit cell with a concentration of 1/8 on the anion site. 12,[48][49][50] Hence, Y 3+ /Ta 5+ are surrounded by seven oxygen atoms (in an 8c Wyckoff position) and a vacancy (7 + 1 coordination, as described by Subramani et al 37 ). Far et al 51 Given that both structures are similar, the main XRD peaks appear at the same 2θ values, so a qualitative analysis does not suffice and may lead to misinterpretation.…”

“…Most authors have dealt with the difference between the A 3+ and B 5+ ionic radii in A 3 BO 7 compounds as being the most important factor driving structure crystallization. Subramani et al 37 showed conditions that can induce disorder in pyrochlore compounds other than the A 3+ and B 5+ ionic radii, including temperature, pressure, ball milling, and radiation damage. Francis et al 16 also observed phase evolution when they varied the dopant concentration in La 3 TaO 7 compounds.…”

Synthesis and Characterization of LaNi0.5Ti0.5O3 and La2NiTiO6 Double Perovskite Nanoparticles

“…Perovskites are materials represented by the formula ABX 3 . A cation can be an alkali, alkali earth, or lanthanide metal, B cations are transition metals, and X can be oxygen or a halide [ 1 ]. The structure can be illustrated by octahedra layers, formed by octahedra sharing vertices, in which X atoms are found.…”

“…The following supporting information can be downloaded at: , Figure S1: Observed (red symbols), calculated (black line), and difference (blue line) XRD profiles of Sample 3, Figure S2: Observed (red symbols), calculated (black line) and difference (blue line) X-ray diffraction profile of Sample 3 using Pbnm space group (ICSD: 88851, [ 1 ]), Figure S3: Both unit-cell parameters and corrected observed 2-theta values based on the Rietveld Refinement of XRD data of Sample 1 to perform the indexation of the corresponding XRD pattern, Figure S4: Both unit-cell parameters and corrected observed 2-theta values based on the Rietveld Refinement of XRD data of Sample 2 to perform the indexation of the corresponding XRD pattern, Figure S5: Both unit-cell parameters and corrected observed 2-theta values based on the Rietveld Refinement of XRD data of Sample 3 to perform the indexation of the corresponding XRD pattern, Figure S6: Unit-cell parameters, the corrected observed and calculated peak positions, and the respective difference obtained from the McMaille software for the case of Sample 1, Figure S7: Unit-cell parameters, the corrected observed and calculated peak positions, and the respective difference obtained from the McMaille software for the case of Sample 2, Figure S8: Unit-cell parameters, the corrected observed and calculated peak positions, and the respective difference obtained from the McMaille software for the case of Sample 3, Figure S9: vs. curve showing the Néel temperature for Sample 1, Figure S10: Variation of M along with M −1 vs. temperature for Sample 2 from 2 to 40 K; Table S1: Structural parameters, average crystallite size, together with conventional discrepancy factors from Rietveld refinement of XRD data for Sample 1, Sample 2, and Sample 3 [ 30 ], Table S2: Structural parameters, results of phase analysis together with conventional discrepancy factors from Rietveld refinement of XRD pattern for Sample 3, Table S3: Bond distances and bond angles for Sample 1, Sample 2, and Sample 3, Table S4: Structural parameters, average crystallite size, together with conventional discrepancy factors from Rietveld refinement of XRD data for Sample 3.…”

Traversing the pyrochlore stability diagram; microwave-assisted synthesis and discovery of mixed B-site Ln$_2$InSbO$_7$ family

“…The flexibility to decorate the frustrated lattice with lanthanide elements of varying single-ion anisotropy, moment size, and radii -combined with the steric and chemical flexibity offered by the B-site -have cemented the pyrochlore family as a fruitful arena for the pursuit of the emergence of exotic and novel magnetic ground states. Experimental and theoretical studies alike have proposed the Ln 2 B 2 O 7 pyrochlores as a means to realize a myriad of properties ranging from unconventional long-range order [2][3][4][5][8][9][10][11][12][13][14][15], unconventional spin-glass behavior [3,[16][17][18][19][20][21][22][23][24][25][26][27], topologically-nontrivial electronic states [28][29][30][31][32][33][34][35][36], spin ices [12,[37][38][39][40][41][42][43][44][45][46][47], magn...…”