BaZr(BO3)2: a non-centrosymmetric dolomite-type superstructure

The investigation of the ternary phase diagram for BaOZrO2B2O3 has allowed single crystals to be grown by the flux method with formula BaZr(BO3)2. As this composition has been already announced in the literature, but without any structural data, the structure of BaZr(BO3)2 has been solved using X-ray data collected on a Kappa CCD diffractometer. This borate crystallizes in the trigonal symmetry with non-centrosymmetric space group R3c (no. 161): a=b=5.167(1) Å and c=33.913(7) Å; Z=6. The structure derived from the dolomite-type with a doubling of the c parameter. Along the c-axis, alternated layers of Ba atoms and Zr atoms are separated by planes of BO3 groups. BaO6 and ZrO6 octahedra so formed are linked by their corners and each Ba(Zr) octahedron is linked to six Zr(Ba) octahedra and to six borate groups. The small deviation from centrosymmetry is attested by considering refinement agreement for the (weak) reflections (h k l) with odd value of l, and positive response of the powder second harmonic generation (SHG) test. A new J.C.P.D.S.-I.C.D.D. card is proposed for this compound.