Abstract
Single crystals of LaNb7O12were obtained by annealing a mixture of La2O3, Nb2O5, and Nb in 1:1:1 molar ratio with NH4Cl in a sealed quartz tube. LaNb7O12crystallizes in the monoclinic space groupP21/cwith cell parametersa= 10.762(1),b= 9.192(1),c= 10.314(1) Å, β = 104.25°, andz= 4 formula units per cell. The structure was determined from single-crystal X-ray diffraction data and refined to a residual ofR(F) = 0.037 andRw(F2) = 0.077 for 119 variable parameters and a unique data set of 1400 observations [I> 2σ(I)]. The essential building units of the structure are Nb6and NbO6octahedra and La ions in eight coordination of oxygen. Two NbO6octahedra corner-share to form a pair and connect with Nb6octahedra via oxygen atoms. Nb6octahedra share both apical and inner oxygen atoms with neighboring Nb6to form columns of Nb6O12clusters along thecaxis. The Nb6O12clusters exhibit 14 valence electrons inM–Mbonding states. LaNb7O12is a semiconductor with an activation energy of 0.08 eV. The magnetic susceptibility data show weak temperature-independent paramagnetism. The Madelung part of the lattice energy has been calculated and is discussed.
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