Structural phase transitions in Ruddlesden-Popper phases of strontium titanate: {\em ab initio} and inhomogeneous Ginzburg-Landau approaches

TL;DR

This study combines ab initio calculations and Ginzburg-Landau modeling to analyze anti-ferrodistortive order in Ruddlesden-Popper phases of strontium titanate, revealing strain-dependent behaviors and size effects.

Contribution

It provides the first systematic ab initio analysis of AFD order in RP phases of SrTiO3 and extends Ginzburg-Landau theory to include inter-octahedral interactions.

Findings

AFD order exists in all RP phases under certain strains

AFD order magnitude scales as 1/n^2 with phase number n

Ginzburg-Landau model accurately reproduces ab initio results

Abstract

We present the first systematic {\em ab initio} study of anti-ferrodistortive (AFD) order in Ruddlesden-Popper (RP) phases of strontium titanate, Sr$_{1+n}$Ti$_n$O$_{3n+1}$, as a function of both compressive epitaxial strain and phase number $n$. We find all RP phases to exhibit AFD order under a significant range of strains, recovering the bulk AFD order as $\sim 1/n^2$. A Ginzburg-Landau Hamiltonian generalized to include inter-octahedral interactions reproduces our {\em ab initio} results well, opening a pathway to understanding other nanostructured perovskite systems.