New transition metal phosphates related to KTiOPO₄. Synthesis of K_0.5M_0.5M'_0.5OPO₄ (M=Nb,Ta; M'=Ti,V) and K_1-xTi_1-xV_xOPO₄ exhibiting nonlinear optical behavior

Abstract

Several transition metal phosphates of the general formula KM_0.5M'_0.5OPO₄, where M = Nb^V or Ta^V and M' = Ti^III, V^III, Cr^III, Fe^III, possessing the KTiOPO₄ (KTP) structure have been synthesized. Unlike KTP, none of these phosphates exhibit second harmonic generation (SHG) of the 1064-nm radiation. Soft-chemical oxidation of the Ti^III and V^III phosphates using chlorine in CHCl₃, however, restores the SHG property to the oxidized materials, K_0.5M_0.5M'_0.5OPO₄ (M = Nb^V, Ta^V; M' = Ti^IV, V^IV). K_1-x Ti_1-xV_xOPO₄ (x ≤ 0.25) prepared similarly from KTi_1-xV_xOPO₄ also exhibit SHG. The results reveal that exclusive presence of d⁰ cations at the Ti^IV site preserves the SHG response of KTP derivatives.