Unconventional Thermal Expansion in quasi-one-dimensional monoclinic BaIrO$_3$

TL;DR

This study reveals an unconventional invar-like thermal expansion in quasi-one-dimensional BaIrO₃, strongly linked to its magnetic transition, challenging traditional models of lattice behavior.

Contribution

It provides the first detailed investigation of the anomalous thermal expansion in BaIrO₃ and its correlation with magnetic and electronic transitions.

Findings

Cell volume deviates from Debye model predictions.

Unconventional thermal expansion begins near magnetic transition.

Strong correlation between lattice behavior and electronic/magnetic structure.

Abstract

We have investigated the temperature dependence of the crystal structure of quasi-one-dimensional monoclinic BaIrO$_3$ using X-ray diffraction. Diffraction patterns were measured across a temperature range from 13 K to 300 K, with 5-degree steps, and Rietveld refinements were performed to extract the relevant lattice parameters. The resulting cell volumes exhibit a significant deviation from the Debye model predictions for lattice-specific heat within a reasonable range of the Debye temperature, Gr{\"u}neisen parameter, and bulk modulus. This suggests an invar-like, unconventional thermal expansion behavior. The deviation begins near the weak ferromagnetic transition temperature, indicating a strong correlation with changes in the electronic and magnetic structure of monoclinic BaIrO$_3$.