Ba₄YZr₃F₂₃and Ba₄LnZr₃F₂₃: a new noncentrosymmetric potential host structure type for optical devices

Abstract

The first ternary BaF 2 -Ln(Y)F 3 -ZrF 4 phases crystallizing near the composition range of fluoride glasses, namely Ba 4 YZr 3 F 23 (barium yttrium fluoridozirconate) and isotypic Ba 4 LnZr 3 F 23 (Ln = Yb, Er and Nd), have been synthesized. The crystal structure of Ba 4 YZr 3 F 23 cannot be correctly determined in the centrosymmetric space group Pnma (R1 = 0.09); it is preferably described in the noncentrosymmetric space group Pn2 1 a (R1 = 0.028). All cations are located at y = 0.25-0.29 and 0.75-0.79. This new structure type is formed by infinite {[YZr 3 F 23 ] 8À } n columns associating, along [001], YF 9 tricapped trigonal prisms, ZrF 8 dodecahedra and ZrF 7 polyhedra. These columns are interconnected via BaF 10+1 and BaF 12 irregular polyhedra.