Structural Phase Transition and Microstructures of Li2CoSiO4

概要

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The orthorhombic Pbn21 phase of Li2CoSiO4 has been prepared by solid state reaction of Li2CO3, CoC2O4・2H2O, and highly dispersed SiO2 at 900 °C and the subsequent slow cooling in Ar gas stream. The DTA curve shows peaks at around 540 °C indicating a reversible structural phase transition. XRD pattern of the sample quenched from 650 °C can be indexed as a Pmn21 phase. However, electron diffraction patterns show complex diffuse scatterings. From the in-situ XRD patterns at high temperature, a reversible second order-type phase transition from Pbn21 to Pmn21 phase was confirmed and it is interpreted as an order-disorder transition of Co and Li atoms. At high temperature, Pmn21 phase transforms to the monoclinic γ-phase with large thermal hysteresis; DTA curve shows peaks at 950°C on heating and at 780°C on cooling.
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