Three new phosphates with isolated P2O7 units: noncentrosymmetric Cs2Ba3(P2O7)2 and centrosymmetric Cs2BaP2O7 and LiCsBaP2O7

Abstract

Three new phosphates, a noncentrosymmetric (NCS) Cs₂Ba₃(P₂O₇)₂ and centrosymmetric (CS) Cs₂BaP₂O₇ and LiCsBaP₂O₇, have been synthesized from high-temperature solutions for the first time. Analysis of the structures determined by single-crystal X-ray diffraction showed that although the three compounds contained isolated P₂O₇ units, they yielded different three-dimensional (3D) networks: Cs₂Ba₃(P₂O₇)₂ crystallized in the NCS Orthorhombic space group P2₁2₁2₁, Cs₂BaP₂O₇ in the CS monoclinic space group P2₁/n, and LiCsBaP₂O₇, having an identical stoichiometry with Cs₂BaP₂O₇, crystallized in monoclinic space group, P2₁/c. Structural comparisons suggested the differences between their 3D frameworks to be due to differences between the sizes and coordination environments of the cations. Characterizations including thermal and optical analyses showed Cs₂Ba₃(P₂O₇)₂ and Cs₂BaP₂O₇ to melt congruently, and Cs₂Ba₃(P₂O₇)₂ to exhibit a wide transparent region with a cut-off edge below 176 nm. The NLO properties and electronic structures of these compounds were investigated using first-principles calcualtions.