A structure and phase analysis investigation of the “1:1” ordered A2InNbO6 perovskites (A=Ca2+, Sr2+, Ba2+)

Rationalization of Double Perovskite Oxides as Energy Materials: A Theoretical Insight from Electronic and Optical Properties

The quest for clean energy conversion has become one of the most important efforts for tackling the greenhouse effect for a sustainable environment. This involves energy-scavenging processes like photovoltaics and catalysis, which have been manifested using the solar spectrum. For high-efficiency and durable conversion processes, the search for the low-cost, stable, and environment-friendly functional materials is elusive. In the field of solar cells and catalysis, double perovskite oxides (DPOs) have emerged as potential candidates in recent years. Through compositional tuning and band gap engineering, a plethora of materials are being developed for pertinent applications in this field of energy. Oxide perovskites possess the advantage of a high carrier lifetime compared to that with halide perovskites, which can be beneficial for energy applications. In this perspective, we have presented theoretical investigations focusing on the different types of double perovskite oxides based on the composition space in a systematic manner. Corresponding electronic and optical properties are discussed along with a future outlook on the novel routes to find efficient members in this family.

Expanding the Doubly Cation Ordered AA'BB'O6 Perovskite Family: Structural Complexity in NaLaInNbO6 and NaLaInTaO6

Two new perovskite compounds, NaLaInNbO₆ and NaLaInTaO₆, have been synthesized. Both compounds have a rock-salt ordering of the In/Nb or In/Ta cations and a layered ordering of the Na/La. They are unusual among this family of doubly cation ordered perovskites for having a +3/+5 combination of B/B' oxidation states instead of a divalent cation and W⁶⁺. Synchrotron powder diffraction and electron diffraction data show both compounds have tetragonal √2a_p × √2a_p × 2a_p unit cells. The octahedral tilt system of these compounds is complicated and seems to vary depending on the length scale considered. Bond valence considerations demonstrate that none of the tilt systems compatible with a tetragonal unit cell produce a stable structure. It is proposed that additional oxygen displacements are occurring on a local scale. The XRD data show that the B-site ordering is nearly complete in both cases, while the A-site cations show a lower degree of order. The tendency of the B'-cation to undergo a second order Jahn-Teller distortion is identified as having an influence over the degree of A-site ordering. Transmission electron microscopy shows fragmentation into nanosized domains with perpendicular orientations of the layered A-site cation ordering. Such structures may be polar over short length scales which could lead to interesting dielectric properties such as relaxor behavior. The prospects for finding new doubly cation ordered perovskites are also discussed.

Theory of order–disorder phase transitions of B-cations in AB′1/2 B′′1/2O3 perovskites

Perovskite-like oxides AB′1/2 B′′1/2O3 with two different cations in the B-sublattice may experience cation order–disorder phase transitions. In many cases the degree of cation ordering can be varied by suitable synthesis conditions or subsequent sample treatment, which has a fundamental impact on the physical properties of such compounds. Therefore, understanding the mechanism of cation order–disorder phase transition and estimation of the phase transition temperature is of paramount importance for tuning of properties of such double perovskites. In this work, based on the earlier proposed cation–anion elastic bonds model, a theory of order–disorder phase transitions of B-cations in AB′1/2 B′′1/2O3 perovskites is presented, which allows reliable estimation of the phase transition temperatures and of the reduced lattice constants of such double perovskites.

Structural dependence of the photocatalytic properties of double perovskite compounds A2InTaO6 (A = Sr or Ba) doped with nickel

Photocatalytic activity is greatly improved when there is no structural distortion, which guarantees maximal metal–oxygen–metal interactions.

Synchrotron X-Ray Powder Diffraction Studies of Structural Phase Transitions in Perovskite Oxides

The utilization of the high resolution powder diffractometer at the Australian Synchrotron to obtain accurate and precise structures of some perovskite-type oxides is described. The structure of CdTiO3 has been studied from room temperature to 1000°C by high-resolution synchrotron X-ray powder diffraction. It was found that CdTiO3 remains orthorhombic in the Pbnm space group over the entire temperature range, with the expansion in the cell volume well fitted to the expression . The magnitudes of the TiO6 tilts are estimated from the refined structural parameters and these progressively reduce as the temperature is increased. The effect of Sr content on the room temperature structure of the double perovskites Ba2–xSrxInTaO6 is also described. At room temperature Ba2InTaO6 crystallizes in a cubic structure in space group . Doping with Sr results in tilting of the corner sharing octahedra with a concurrent lowering of symmetry with the sequence of structures being