Department of Chemistry, University of Houston, 136 Fleming Building, Houston, Texas 77204-5003, USA.
Inorg Chem. 2011 Sep 5;50(17):8663-70. doi: 10.1021/ic2012217. Epub 2011 Jul 29.
The synthesis and characterization of ACuTe(2)O(7) (A = Sr(2+), Ba(2+), or Pb(2+)) have been carried out. Interestingly, SrCuTe(2)O(7) and PbCuTe(2)O(7) are centrosymmetric and isostructural, whereas BaCuTe(2)O(7) is noncentrosymmetric and polar. All of the materials contain CuTe(2)O(7) layers stacked along the b-axis direction that are separated by the "A" cations. The layers are composed of corner-shared CuO(5), TeO(6), and TeO(4) 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 BaCuTe(2)O(7), second-harmonic generation (SHG), piezoelectric, and polarization measurements were performed. A moderate SHG efficiency of approximately 70 × α-SiO(2) was measured. In addition, we determined that BaCuTe(2)O(7) is not ferroelectric; that is, the macroscopic polarization is not reversible. For BaCuTe(2)O(7), 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: SrCuTe(2)O(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) Å(3), and Z = 4; PbCuTe(2)O(7), 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) Å(3), and Z = 4.
已合成并表征了 ACuTe(2)O(7)（A = Sr(2+)、Ba(2+)或 Pb(2+)）。有趣的是，SrCuTe(2)O(7)和 PbCuTe(2)O(7)是中心对称且同构的，而 BaCuTe(2)O(7)是非中心对称且极性的。所有材料均含有沿 b 轴方向堆叠的CuTe(2)O(7)层，这些层由"A"阳离子隔开。这些层由共用角的 CuO(5)、TeO(6)和 TeO(4)多面体组成。“A”阳离子对极性的影响通过键价概念来描述，包括键应变指数和全局不稳定性指数。对所有三种材料均进行了红外、紫外-可见、热重、差热分析和磁测量。对于 BaCuTe(2)O(7)，还进行了二次谐波产生 (SHG)、压电和极化测量。测量得到的 SHG 效率约为 70 × α-SiO(2)。此外，我们确定 BaCuTe(2)O(7)不是铁电体，即宏观极化不可逆转。对于 BaCuTe(2)O(7)，在 90°C 下，测得的热释电系数为-9.5 μC/m(2)·K，压电电荷系数为 49 pm/V。晶体数据如下：SrCuTe(2)O(7)，正交晶系，空间群 Pbcm（No. 57），a = 7.1464(7)Å，b = 15.0609(15)Å，c = 5.4380(5)Å，V = 585.30(10)Å(3)，Z = 4；PbCuTe(2)O(7)，正交晶系，空间群 Pbcm（No. 57），a = 7.2033(5)Å，b = 15.0468(10)Å，c = 5.4691(4)Å，V = 592.78(7)Å(3)，Z = 4。
