Materials Data on CaNb2Bi2O9 by Materials Project

Abstract

CaBi2Nb2O9 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one BiO2 sheet oriented in the (0, 0, 1) direction and one CaNb2O5 sheet oriented in the (0, 0, 1) direction. In the BiO2 sheet, Bi3+ is bonded in a 4-coordinate geometry to eight O2- atoms. There are a spread of Bi–O bond distances ranging from 2.33–2.92 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to four equivalent Bi3+ atoms. In the second O2- site, O2- is bonded to four equivalent Bi3+ atoms to form a mixture of edge and corner-sharing OBi4 tetrahedra. In the CaNb2O5 sheet, Ca2+ is bonded to twelve O2- atoms to form CaO12 cuboctahedra that share corners with four equivalent CaO12 cuboctahedra, faces with four equivalent CaO12 cuboctahedra, and faces with eight equivalent NbO5 square pyramids. There are eight shorter (2.73 Å) and four longer (2.77 Å) Ca–O bond lengths. Nb5+ is bonded to five O2- atoms to form NbO5 square pyramids that share corners with five equivalent NbO5 square pyramids and faces with four equivalent CaO12 cuboctahedra. There is four shorter (1.96 Å) and one longer (1.97 Å) Nb–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to four equivalent Ca2+ and two equivalent Nb5+ atoms. In the second O2- site, O2- is bonded in a distorted linear geometry to two equivalent Ca2+ and two equivalent Nb5+ atoms.