Hydrothermal synthesis of KTi2(PO4)3, α-Ti(HPO4)2·H2O and γ-Ti(PO4)(H2PO4)·2H2O from a lepidocrocite-type titanate

ABSTRACT A potassium titanium phosphate, KTi2(PO4)3, and two types of hydrated titanium phosphates, α-Ti(HPO4)2·H2O and γ-Ti(PO4)(H2PO4)·2H2O, were prepared by hydrothermal reaction using a layered lepidocrocite-type titanate as a starting compound. When layered lepidocrocite-type K0.7(Li,Ti)2O4 (Lss; Ohtsuka Chemical Co., Ltd.) was used at a reaction temperature of 180°C, KTi2(PO4)3 was obtained. The crystal structure of KTi2(PO4)3 was a NASICON-like rhombohedral one with a low thermal expansion coefficient. The thermal expansion coefficient of KTi2(PO4)3 was determined using synchrotron X-ray powder diffraction data (SRXD), and the thermal expansion coefficients for the a-axis, c-axis and unit cell volume were ？2.82 x 10？6, 7.16 × 10？6 and 1.49 × 10？6 K？1, respectively. Two types of layered titanium phosphates, α-Ti(HPO4)2·H2O and γ-Ti(PO4)(H2PO4)·2H2O, were prepared by hydrothermal reaction using protonated titanate (Lss-H) derived from lepidocrocite-type potassium titanate (Lss) by the ion-exchange reaction