SYNTHESIS, STRUCTURE, AND PROPERTIES OF A NEW T-STAR STRUCTURE COPPER-OXYCHLORIDE OF MLNCUO3CL (M = CA, SR AND LN = ND, SM, EU, GD)

The syntheses of a new copper oxychloride with the general formula of MLnCuO3Cl (M = Ca, Sr and Ln =Nd, Sm, Eu, Gd) are reported. These compounds are shown to have the T* structure where the copper atoms are coordinated by a square pyramidal geometry with a chloride ion in the apical position. This structure is supported by the X-ray powder patterns and lattice parameters of the new oxychlorides. The substitution of Sr for Ca in Ca1-xSrxLnCuO3Cl with Ln =Nd, Sm was performed, and the substitution is discussed in terms of the size requirements of the T* structure. Alternating current impedance measurements for CaSmCuO3Cl and Ca0.72Sr0.28NdCuO3Cl from 100 to 600°C are presented; when annealed in oxygen, CaSmCuO3Cl showed semiconducting behavior with an activation energy of 0.12 eV. When these two samples were annealed in argon, ionic conductivity from oxygen vacancies was observed. Magnetic susceptibility measurements for CaSmCuO3Cl and Ca0.72Sr0.28NdCuO3Cl from 2 to 400 K show similarity to the magnetic results for Sm2CuO4 and Nd2CuO4, respectively. The resistivity and magnetic measurements indicate that the properties of these compounds are similar to those of their parent copper oxides, Ln2CuO4, and not to their parent oxychlorides, M2CuO2Cl2 (M =Ca, Sr). © 1991 Academic Press, Inc.