American Chemical Society
cm7019334_si_004.cif (10.58 kB)

(NH4)2Te2WO8:  A New Polar Oxide with Second-Harmonic Generating, Ferroelectric, and Pyroelectric Properties

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posted on 2007-11-13, 00:00 authored by Jun-Ho Kim, Jaewook Baek, P. Shiv Halasyamani
A new polar ammonium tungsten tellurite, (NH4)2Te2WO8, has been synthesized and structurally characterized. The material was synthesized hydrothermally, using NH4OH, WO3, and TeO2 as reagents, and structurally characterized by single-crystal X-ray diffraction. (NH4)2Te2WO8 crystallizes in the noncentrosymmetric (NCS) polar monoclinic space group P21 (No. 4) with a = 6.9716(9) Å, b = 7.0279(9) Å, c = 9.4593(13) Å, and β = 99.188(2)°. The material exhibits a two-dimensional structure consisting of WO6 octahedra connected to TeO4 polyhedra. Both the W6+ and the Te4+ cations are in asymmetric coordination environments attributable to second-order Jahn−Teller (SOJT) effects. (NH4)2Te2WO8 is NCS; thus second-harmonic generation (SHG) measurements were performed. SHG experiments, using 1064 nm radiation, revealed an efficiency of approximately 250 × α-SiO2. As (NH4)2Te2WO8 is also polar, ferroelectric and pyroelectric measurements were performed. A ferroelectric hysteresis loop (polarization vs electric field) was observed, indicating the dipole moment in (NH4)2Te2WO8 is “switchable”. A spontaneous polarization (Ps) of 0.19 μC/cm2 was measured. In addition, the pyroelectric coefficient (total effect), p, was determined to be −0.22 μC/m2·K at 50 °C.