The synthesis and characterization of ACuTe2O7 (A = Sr2+, Ba2+, or Pb2+) have been carried out. Interestingly, SrCuTe2O7 and PbCuTe2O 7 are centrosymmetric and isostructural, whereas BaCuTe 2O7 is noncentrosymmetric and polar. All of the materials contain [CuTe2O7]2- layers stacked along the b-axis direction that are separated by the "A" cations. The layers are composed of corner-shared CuO5, TeO6, and TeO4 polyhedra. The influence of the "A" cation on the polarity is described by bond valence concepts, including the bond strain index and global instability index. Infrared, UV-vis, thermogravimetric, differential thermal analysis, and magnetic measurements were performed on all three materials. For BaCuTe2O7, second-harmonic generation (SHG), piezoelectric, and polarization measurements were performed. A moderate SHG efficiency of approximately 70 × α-SiO2 was measured. In addition, we determined that BaCuTe2O7 is not ferroelectric; that is, the macroscopic polarization is not reversible. For BaCuTe2O7, a pyroelectric coefficient of-9.5 μC/m 2·K at 90 °C and a piezoelectric charge coefficient of 49 pm/V were determined. Crystal data are the following: SrCuTe2O 7, orthorhombic, space group Pbcm (No. 57), a = 7.1464(7) Å, b = 15.0609(15) Å, c = 5.4380(5) Å, V = 585.30(10) Å3, and Z = 4; PbCuTe2O7, orthorhombic, space group Pbcm (No. 57), a = 7.2033(5) Å, b = 15.0468(10) Å, c = 5.4691(4) Å, V = 592.78(7) Å3, and Z = 4. © 2011 American Chemical Society.
