Long-range and local crystal structures of the Sr1-xCaxRuO3 Perovskites

TL;DR

This study combines long-range and local structural probes to analyze the crystal structures of Sr1-xCaxRuO3 perovskites, revealing orthorhombic global structure with locally monoclinic features and random nanoscale cation distribution.

Contribution

It provides a comprehensive structural analysis using multiple techniques, highlighting local monoclinic distortions and nanoscale cation randomness in Sr1-xCaxRuO3 perovskites.

Findings

Materials are globally orthorhombic at high resolution.

Locally monoclinic structures are observed via pair distribution function analysis.

No phase transitions occur between 80 and 300 K for intermediate compositions.

Abstract

The crystal structures of the Sr1-xCaxRuO3 perovskites are investigated using both long range and local structural probes. High resolution synchrotron powder X-ray diffraction characterization at ambient temperature shows that the materials are orthorhombic to high precision, and we support previous work showing that Ca2+ substitution for Sr2+ primarily changes the tilting of rigid corner-sharing RuO6 octahedra at their shared oxygen vertices. X-ray pair distribution function analysis for SrRuO3, CaRuO3 and one intermediate composition show them to be locally monoclinic, and no long range or local phase transitions are observed between 80 and 300 K for materials with intermediate compositions. High-resolution transmission electron microscopy shows that the Sr/Ca distribution is random at the nanoscale. We plot magnetic characteristics such as the ferromagnetic Tc, Curie-Weiss theta, effective moment, and ambient temperature susceptibility vs. the octahedral tilt and unit cell volume.