High-pressure synthesis, crystal structure, and properties of the new orthorhombic rare-earth meta-oxoborates RE(BO2)3 (RE = Dy-Lu)

The new orthorhombic meta-oxoborates RE(BO2)(3) (equivalent to REB3O6) (RE = Dy-Lu) have been synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 degreesC. They are isotypic to the known ambient pressure phase Tb(BO2)(3), space group Pnma. In contrast to Dy(BO2)(3), which was also obtained in small amounts under high-temperature conditions, the preparation of the higher orthorhombic homologues RE(BO2)(3) (RE = Ho-Lu) was only possible using high-pressure. The meta-oxoborates RE(BO2)(3) (RE = Dy-Er) were synthesized as pure products, whereas the orthorhombic phases with RE = Tm-Lu were only obtained as byproducts. With the exception of Yb(BO2)(3) it was possible to establish single crystal data for all compounds. The results of temperature-resolved in-situ powder-diffraction measurements, DTA, IR-spectroscopic investigations, and magnetic properties are also presented.