PASCal: A principal-axis strain calculator for thermal expansion and compressibility determination

TL;DR

PASCal is a web-based tool that simplifies calculating principal thermal expansion and compressibility coefficients from lattice data, revealing new scientific insights in materials with anisotropic properties.

Contribution

The paper introduces PASCal, a novel web tool that re-analyzes lattice data to uncover previously unnoticed anisotropic thermal and mechanical behaviors in materials.

Findings

Cu-SIP-3 exhibits the strongest area-negative thermal expansion observed

HMX shows stronger mechanical anisotropy and uniaxial NTE than expected

Malayaite displays a strong negative linear compressibility due to polyhedral tilting

Abstract

We describe a web-based tool (PASCal; Principal Axis Strain Calculator) aimed at simplifying the determination of principal coefficients of thermal expansion and compressibilities from variable-temperature and variable-pressure lattice parameter data. In a series of three case studies, we use PASCal to re-analyse previously-published lattice parameter data and show that additional scientific insight is obtainable in each case. First, the two-dimensional metal-organic framework Cu-SIP-3 is found to exhibit the strongest area-negative thermal expansion (NTE) effect yet observed; second, the widely-used explosive HMX exhibits much stronger mechanical anisotropy than had previously been anticipated, including uniaxial NTE driven by thermal changes in molecular conformation; and, third, the high-pressure form of the mineral malayaite is shown to exhibit a strong negative linear compressibility (NLC) effect that arises from correlated tilting of SnO6 and SiO4 coordination polyhedra.