Structural Phase Transitions of Li₂MgSiO₄ and Li₂MgGeO₄

抄録

Structural phase transitions of Li₂MgSiO₄ and Li₂MgGeO₄ at high temperature have been investigated by means of in situ high temperature powder XRD measurements. The monoclinic P2₁/n phase of Li₂MgSiO₄ shows a reversible phase transition to high temperature orthorhombic Pmnb phase due to the order-disorder of Mg and Li atoms at 590 ℃. By slow cooling from 1000℃ to room temperature, the monoclinic Pn phase of Li₂MgGeO₄ was obtained. Lattice parameters are a = 6.389(1), b = 5.475(1), c = 4.995(1) Å, and β = 90.18(1). The monoclinic Pn phase of Li₂MgGeO₄ shows a reversible transformation to the orthorhombic Pmn2₁ phase at 540 ℃, accompanied with the abrupt contraction along c-axis and elongation along b-axis on heating.