Thermomechanical properties of zero thermal expansion materials from theory and experiments

TL;DR

This study combines experiments and first-principles simulations to analyze the anisotropic thermomechanical properties of Ba1-xSrxZn2Si2O7, revealing how composition influences negative thermal expansion and elastic behavior.

Contribution

It provides a comprehensive understanding of the origin and composition dependence of thermomechanical properties in BZS, integrating experimental data with ab initio molecular dynamics and phonon calculations.

Findings

NTE decreases with increasing Sr content

Vibrational density of states shifts to higher frequencies with Sr substitution

NTE is mainly due to deformation of SiO4 and ZnO4 tetrahedral rings

Abstract

Origin and composition dependence of the anisotropic thermomechanical properties are elucidated for Ba1-xSrxZn2Si2O7 (BZS) solid solutions. The high-temperature phase of BZS shows negative thermal expansion (NTE) along one crystallographic axis and highly anisotropic elastic properties characterized by X-ray diffraction experiments and simulations at the density functional theory level. Ab initio molecular dynamics simulations provide accurate predictions of the anisotropic thermal expansion in excellent agreement with experimental observations. The NTE considerably decreases with increasing Sr content x. This is connected with the composition dependence of the vibrational density of states (VDOS) and the anisotropic Gr\"uneisen parameters. The VDOS shifts to higher frequencies between 0-5 THz due to substitution of Ba with Sr. In the same frequency range, vibrational modes contributing most to the NTE are found. In addition, phonon calculations using the quasi-harmonic approximation revealed that the NTE is mainly connected with deformation of four-membered rings formed by SiO4 and ZnO4 tetrahedra. The thermomechanical and vibrational properties obtained in this work provide the basis for future studies facilitating the targeted design of BZS solid solutions as zero or negative thermal expansion material.