Unusual Isomorphism in the Structure of K3(Yb0.84Nb0.1□0.06)[Si3O8(OH)2]: a New Representative of the Germanate-Silicate Family

Crystals of the new silicate K3(Yb0.84Nb0.1□0.06)[Si3O8(OH)2] are synthesized hydrothermally at a temperature of 280 °C and a pressure of 100 atm. Its structure belongs to the known structure type of mixed layer silicates K3RESi3O8(OH)2, where RE = Y, Ho, Eu, Er Gd, Tb, Dy. The layers consist of chains of triorthogroups of Si tetrahedra that “embrace” isolated (Yb,Nb) octahedra. The K atoms are in and between the layers. The most interesting feature of the new crystals established for the first time is isomorphic incorporation of Nb atoms into the site occupied by Yb ions, which requires the presence of a vacancy at the octahedral position to compensate for the charge.