Structure prediction of ordered and disordered multiple octahedral cation perovskites using SPuDS

Area of Science:

• Crystallography
• Materials Science
• Computational Chemistry

Background:

• The SPuDS software package has demonstrated accuracy in predicting crystal structures of AMX(3) and A(1 - x)A'(x)MX(3) perovskites with octahedral tilting.
• Ordered double perovskites, A(2)MM'X(6), often exhibit octahedral tilting distortions, with approximately 70% of known structures featuring such distortions.
• Five dominant tilt systems (Fm\overline 3m, I4/m, R\overline 3, I2/m, P2(1)/n) account for nearly all reported ordered perovskite structures.

Purpose of the Study:

• To extend the SPuDS software's predictive capabilities to ordered double perovskites (A(2)MM'X(6)).
• To assess the accuracy of SPuDS in predicting crystal structures of ordered double perovskites, including those with octahedral tilting.
• To compare octahedral tilting modes in ordered double perovskites with those in AMX(3) perovskites and examine unit-cell pseudosymmetry.

Main Methods:

• Extension of the SPuDS software to handle the aristotype Fm\overline 3m cubic structure of A(2)MM'X(6) compounds.
• Calculation of crystal structures for seven distinct octahedral tilting systems, including the five dominant ones.
• Comparison of SPuDS-predicted structures with experimentally reported crystal structures of ordered double perovskites.

Main Results:

• SPuDS accurately predicts crystal structures of A(2)MM'X(6) ordered double perovskites, particularly those with octahedral tilting distortions.
• The software can calculate structures for five dominant and two additional octahedral tilting systems.
• Sr-containing double perovskites exhibit a stronger tendency towards unit-cell pseudosymmetry compared to Ca-containing analogues.

Conclusions:

• The SPuDS software is a reliable tool for predicting crystal structures of ordered double perovskites with octahedral tilting.
• The study provides insights into the favored octahedral tilting modes in double perovskites and their comparison with AMX(3) perovskites.
• Differences in pseudosymmetry tendencies between Sr- and Ca-based double perovskites are highlighted.