High-Dielectric-Constant Oxide Nd 2 Ba 2 CaZn 2 Ti 3 O 14.4 Forms as a Disordered Perovskite
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High-Dielectric-Constant Oxide Nd2Ba2CaZn2Ti3O14.4 Forms as a Disordered Perovskite P. Jha and A. Ganguli of the Department of Chemistry at the Indian Institute of Technology, S. Bobev at Los Alamos National Laboratory, and G. Subbanna in the Materials Research Center at the Indian Institute of Science have prepared and characterized an oxide with the formula Nd2Ba2CaZn2Ti3O14.4 in an attempt to produce an oxide with a high dielectric constant and low dielectric loss. As reported in the June 3 issue of Chemistry of Materials, the oxide was prepared by a high-temperature ceramic route at 1200°C and characterized by x-ray, neutron, and electron diffraction studies as well as by scanning electron microscopy and studies of the frequency and temperature—dependence of the dielectric properties. The diffraction studies indicate that the oxide has a disordered perovskite structure with a cubic cell lattice parameter of ~3.94 Å, significantly less than the ~4.00 Å lattice parameter of the simple cubic perovskite BaTiO3. The preliminary characterization of the dielectric properties of Nd2Ba2CaZn2Ti3O14.4 is promising, according to the researchers, as the compound displays a combination of high dielectric constant, low dielectric loss, and stability with regard to frequency. At 100 kHz, the dielectric constant varied from 59 (at 35°C) to 62 (at 300°C). The corresponding dielectric loss at these temperatures varied from 0.0047 to 0.03033. The researchers said that there is likely a loss peak at or near 500 kHz. Furthermore, the dielectric constant was nearly stable over a frequency range of 0.5–500 kHz at room temperature. Additional characterization studies are needed to determine the thermal expansion, mechanical strength, and optimal thin-film fabrication conditions. From a materials standpoint, oxides with complex perovskite structures hold tremendous interest. Their promise as advanced materials for applications as magnetic materials, superconductors, and dielectrics has motivated their development. A variety of rare-earth copper titanates have been synthesized earlier in the search for high-temperature superconductors wherein the partially filled copper d-band holds potential for creating novel conducting or superconducting materials. In the present study, the researchers were more interested in dielectric properties of the oxides. As a consequence, they introduced closed-shell zinc in place of the open-shell copper with the goal of producing a high-dielectric-constant material with low dielectric loss. “We are excited by the potential for 470
this new oxide as a very efficient dielectric, especially in the microwave region,” said Ganguli. “We look forward to exploring the range of properties of this material and hope to find it suitable for the electronic industry. New materials continue to pave the way for exciting new technologies, and I am hopeful that Nd2Ba2CaZn2Ti3O14.4 will be useful in this respect.” EMILY JARVIS
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