First-Principles Calculation of Elastic Properties in Li_xZn_1−xO:Nd³⁺ Mechanoluminescence Material

In this study, the elastic properties of the newly discovered mechanoluminescence (ML) material Li_xZn_1−xO:Nd³⁺ are investigated by first-principles calculations. The elastic properties such as Young's modulus, bulk modulus, and shear modulus are calculated from the elastic tensor. As a result of investigating the phase stability of Li_xZn_1−xO:Nd³⁺, it indicates that the wurtzite ZnO phase is stable in the Li additive range of 0 ≤ x ≤ 0.44, and an excess addition caused a structural transition to the h-BN structure. Besides, elastic properties, such as Young's modulus, bulk modulus, and shear modulus of Li_xZn_1−xO:Nd³⁺ are decreased with increasing Li concentration in the examined range of 0 ≤ x ≤ 0.44. Furthermore, it reveals from bonding analysis between cation and anion that the bonding strength of Li─O bonding for the covalent bonding is weaker than that of Zn─O bonding. The elastic softening derives from atomic interaction in the covalent bonding. Therefore, it concludes that elastic softening is promoted by the increase in Li─O bonding with weak covalent bonding as the Li concentration increases.