Pyroelectric Nd(IO3)3⋅H2O. Crystal structure of the transition-metal iodates. II

Abstract

Neodymium iodate monohydrate, Nd(IO3)3⋅H2O, crystallizes in the monoclinic system with space group P21 and two formulas in the unit cell. The pyroelectric coefficient at room temperature is about 2.2×10−5 cm−2/°K. The lattice constants at 298°K are a = 10.2012±0.0013, b = 6.70530±0.00004, c = 7.3538±0.0009 Å, and β = 113.11±0.02° (λ CuKα1 = 1.540562 Å). A total of 8060 reflections were measured within a reciprocal hemisphere having (sin ϑ)/λ ? 1.02 Å−1, using PEXRAD. The crystal structure was solved by the interpretation of Patterson and Fourier series and refined by the method of least squares using 2603 independent Fmeas, with final agreement factor R = 0.058. The three independent IO3− ions share oxygen atoms to form a three−dimensional framework of corner−sharing polyhedra. Two iodine atoms are coordinated by seven and the third by six oxygen atoms. All iodine polyhedra have three short I−O distances averaging about 1.81 Å, and longer I−O distances ranging to 3.3 Å. The water molecule links all three independent iodate groups together. Nd3+ occupies a distorted bicapped trigonal prism with average Nd−O distance of 2.45 Å . The piezoelectric coefficient d22 is strong and readily detected.