Department of Chemistry, University of Houston, 136 Fleming Building, Houston, Texas 77204-500, United States.
Inorg Chem. 2012 Feb 20;51(4):2662-8. doi: 10.1021/ic202602q. Epub 2012 Feb 1.
Two new noncentrosymmetric (NCS) polar oxides, BaMgTe(2)O(7) and BaZnTe(2)O(7), have been synthesized and characterized, with their crystal structures determined by single crystal X-ray diffraction. The iso-structural materials exhibit structures consisting of layers of corner-shared MgO(5) or ZnO(5), Te(6+)O(6), and Te(4+)O(4) polyhedra that are separated by Ba(2+) cations. The Te(4+) cation is found in a highly asymmetric and polar coordination environment attributable to its stereoactive lone-pair. The alignment of the individual TeO(4) polar polyhedra results in macroscopic polarity for BaMgTe(2)O(7) and BaZnTe(2)O(7). Powder second-harmonic generation (SHG) measurements revealed a moderate SHG efficiency of approximately 5 × KDP (or 200 × α-SiO(2)) for both materials. Piezoelectric charge constants of 70 and 57 pm/V, and pyroelectric coefficients of -18 and -10 μC·m(-2)·K(-1) were obtained for BaMgTe(2)O(7) and BaZnTe(2)O(7), respectively. Although the materials are polar, frequency dependent polarization measurements indicated that the materials are not ferroelectric, that is, the observed macroscopic polarization cannot be reversed. Infrared, UV-vis diffuse spectroscopy, and thermal properties were also measured. Crystal data: BaMgTe(2)O(7), orthorhombic, space group Ama2 (No. 40), a = 5.558(2) Å, b = 15.215(6) Å, c = 7.307(3) Å, V = 617.9(4) Å(3), and Z = 4; BaZnTe(2)O(7), orthorhombic, space group Ama2 (No. 40), a = 5.5498(4) Å, b = 15.3161(11) Å, c = 7.3098(5) Å, V = 621.34(8) Å(3), and Z = 4.
已合成并表征了两种新的非中心对称（NCS）极性氧化物 BaMgTe(2)O(7) 和 BaZnTe(2)O(7)，其晶体结构通过单晶 X 射线衍射确定。同构材料的结构由角共享的 MgO(5) 或 ZnO(5)、Te(6+)O(6) 和 Te(4+)O(4) 多面体层组成，这些多面体层被 Ba(2+) 阳离子隔开。Te(4+) 阳离子处于高度不对称和极性的配位环境中，这归因于其立体活性孤对电子。单独的 TeO(4) 极性多面体的排列导致 BaMgTe(2)O(7) 和 BaZnTe(2)O(7) 具有宏观极性。粉末二次谐波产生 (SHG) 测量表明，这两种材料的 SHG 效率约为 5 × KDP（或 200 × α-SiO(2))。获得了 BaMgTe(2)O(7) 和 BaZnTe(2)O(7) 的压电电荷常数分别为 70 和 57 pm/V，热释电系数分别为-18 和-10 μC·m(-2)·K(-1)。尽管这些材料是极性的，但频率相关的极化测量表明这些材料不是铁电的，也就是说，观察到的宏观极化不能反转。还测量了红外、紫外-可见漫反射光谱和热性能。晶体数据：BaMgTe(2)O(7)，正交晶系，空间群 Ama2（No.40），a = 5.558(2) Å，b = 15.215(6) Å，c = 7.307(3) Å，V = 617.9(4) Å(3)，Z = 4；BaZnTe(2)O(7)，正交晶系，空间群 Ama2（No.40），a = 5.5498(4) Å，b = 15.3161(11) Å，c = 7.3098(5) Å，V = 621.34(8) Å(3)，Z = 4。
