Isomorphous substitution in non-linear optical KTiOPO4: powder diffraction studies of K0.5RB0.5SnOPO4, K0.5Na0.5 Ti0.5Sn0.5OPO4, Na0.5Rb0.5 Ti0.5Sn0.5OPO4 and K0.5Rb0.5 Ti0.5Sn0.5OPO4

Abstract

The structures of K_0.5Rb_0.5SnOPO₄, K_0.5Na_0.5Ti_0.5Sn_0.5OPO₄, Na_0.5Rb_0.5Ti_0.5Sn_0.5OPO₄ and K_0.5Rb_0.5Ti_0.5Sn_0.5OPO₄ have been determined through joint Rietveld analysis of time-of-flight neutron and X-ray powder diffraction data: Pn2₁a, K_0.5Rb_0.5SnOPO₄a= 13.2382(4)Å, b= 10.7083(3)Å, c= 6.5581(2)Å, V= 929.66(6)ų; K_0.5Na_0.5Ti_0.5Sn_0.5OPO₄a= 12.8826(4)Å, b= 10.6384(4)Å, c= 6.3898(2)Å, V= 875.72(8)ų; Na_0.5Rb_0.5 Ti_0.5Sn_0.5OPO₄a= 13.1435(5)Å, b= 10.6433(3) A, c= 6.5478(3)Å, V= 915.97(4)ų; K_0.5Rb_0.6Ti_0.5Sn_0.5OPO₄a= 13.0440(5)Å, b= 10. 6304(4)Å, c= 6. 4961(3)Å, V= 900. 8(1)ų. The ordering of Na in other KTP isomorphs is reduced by Sn substitution into the framework, while the partial cation ordering seen in K_0.6Rb_0.5TiOPO₄ decreases only slightly in K_0.5Rb_0.5Ti_0.5Sn_0.5OPO₄. The preference of Sn for one of the two Ti sites, Ti(2), is unaltered by substitution for K.