High-pressure/high-temperature synthesis of a new polymorphic series of lanthanoid cadmium borates, LnCdB₆O₁₀(OH)₃ (Ln = Sm–Er)

We report on the synthesis, structure determination, and characterization of a new series of compounds Ln CdB 6 O 10 (OH) 3 ( Ln = Sm–Er). Syntheses were carried out in a Walker-type multianvil device at 7 GPa and 650 °C. Structure determinations revealed the coexistence of an orthorhombic and a monoclinic polymorph, depending on the ionic radius of the lanthanoid cation. The orthorhombic structural variants crystallize non-centrosymmetrically in the space group Pna 2 1 (no. 33), while the monoclinic modifications crystallize in space group P 2 1 / c (no. 14). Both modifications display a layered crystal structure built up by a repeating [B 6 O 13 ] 8− building block as their main structural feature.