Synthesis and crystal structure of the new high-pressure phase CdB2O4.

The use of high-pressure/high-temperature conditions (7.5 GPa and 1100 degrees C; Walker-type multianvil apparatus) led to the synthesis of a new cadmium borate CdB2O4, starting from stoichiometric mixtures of the oxides. The crystal structure was determined on the basis of single crystal X-ray diffraction data, to reveal the hexagonal space group P6(3) with a=885.2(2), c=716.72(8) pm, Z=8, R1=0.0178, and wR2=0.0388 (all data). CdB2O4 is built up from interconnected layers of BO4-tetrahedra and exhibits for the first time the basic structure of a family of compounds, represented by BaGa2O4, KAlSiO4, KGeAlO4, KCoPO4, CaP2N4 and the recently discovered SrP2N4. The lack of superstructure ordering in CdB2O4 was confirmed by electron diffraction. Additionally, a B--O--B angle of 180 degrees was found in this borate for the first time.