Pressure-sensitive germanate glass-Li ₂ GeO ₃ , a multifunctional energy material: a theoretical study

From recent research findings, toxic compounds have sparked a lot of interest in theoretical and experimental research as a result of their great potential for harvesting and generating energy from multiple sources at a higher power conversion rate. Despite their great energy production, their hazardous nature limits their practical usage. To overcome this issue, toxic materials can be replaced with more environmentally friendly alternatives, such as germanate glass, even if their power conversion rate is limited. In this article, the adjustment of properties that thereby improves the efficiency of the proposed material, <i>i.e.</i> germanate glass-Li2GeO3 is performed by inducing compressive isotropic pressures using DFT simulation. Herein, interesting results of electronic and structural phase transitions from indirect → direct at P=11 GPa and from orthorhombic → tetragonal structures at P=50 GPa, respectively, are reported. For stability, we present the dynamical, thermal and mechanical stabilities by computing the phonon dispersion curves, MD simulation calculated at room temperature and the elastic constants. An anomalous behaviour of the investigated compound at P∼10–11 GPa has been identified and thoroughly discussed. The piezoelectric response improves with pressure, with the maximum piezoelectric constant, e33=1.42 Cm−2 at P=15 GPa. The orthorhombic-Li2GeO3 being with higher electromechanical conversion rate than its tetragonal phase by more than 10-fold reveals a superior piezoelectric performance of the orthorhombic phase. To the best of our knowledge, the present literature represents the first theoretical analysis of TE properties for this type of material. The calculated TE efficiency using GGA+SOC formalism at T=1200 K is ZT∼0.63 and 0.72 for pristine orthorhombic (P=0 GPa) and tetragonal (P=50 GPa) structures, respectively. The maximum TE efficiency achieved at P=15 GPa yields ZT=0.97 and 1.56 using the GGA and GGA + SOC formalisms.