Unraveling Superior Elasticity and Controlled Thermal Expansion in Trigonal MBO3 (M=Al, Ga) with Isolated [BO3] Group: A Theoretical Perspective

Abstract A comprehensive theoretical investigation employing density functional theory explores the electronic structure, temperature‐dependent elasticity, thermodynamic properties, and chemical bonding of trigonal MBO 3 (M=Al, Ga) with isolated [BO 3 ] groups. The results uncover MBO 3 (M=Al, Ga) as indirect semiconductors with superior mechanical stability, characterized by greater resistance to volume compression over shear deformation. Their elasticity exhibits relatively weak temperature dependence, suggesting excellent thermal stability. Thermodynamic analysis predicts that GaBO 3 has a higher thermal expansion coefficient than AlBO 3 , approximately 2.1×10 −5 K −1 and 1.8×10 −5 K −1 at 300 K, respectively. Significantly, the overall thermal expansion coefficients of GaBO 3 and AlBO 3 are lower compared to other borate materials containing isolated [BO 3 ] groups. Chemical bonding insights reveal that GaBO 3 ′s larger thermal expansion is attributed to its larger atomic displacement parameters and weaker Ga−O bond strength. This research positions MBO 3 (M=Al, Ga) as prime candidates for optical device applications due to their well‐characterized elasticity and controlled thermal expansion.