Synthesis, Structural Characterization, and Electrical Properties of New Oxygen-Deficient Tetragonal Tungsten Bronzes Ba2NdTi2+xNb3鈥?i>xO15鈥?i>x/2<

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• 作者：Marta Prades ; Nahum Mas贸 ; H茅ctor Beltr谩n ; Eloisa Cordoncillo ; Anthony R. West
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：February 18, 2013
• 年：2013
• 卷：52
• 期：4
• 页码：1729-1736
• 全文大小：507K
• 年卷期：v.52,no.4(February 18, 2013)
• ISSN：1520-510X

文摘

Oxygen-deficient tetragonal tungsten bronzes ceramics with general formula Ba₂NdTi_2+xNb_3鈥?i>xO_15鈥?i>x/2 (0 鈮?x 鈮?1) have been prepared by low temperature solvothermal synthesis with final firing of ceramics at 1100鈥?300 掳C in air. Rietveld refinement of X-ray powder diffraction (XRD) and neutron powder diffraction (ND) data at room temperature of Ba₂NdTi₃Nb₂O_14.5 shows that Ba and Nd are ordered on the 15-coordinate and 12-coordinate sites, respectively, Ti and Nb are disordered nonrandomly over the two octahedral sites, and oxygen vacancies locate preferentially in the coordination sphere of Nd and Ti/Nb(2) atoms. Variable frequency impedance measurements show that samples are poor electronic conductors with activation energies 0.8鈥?.7 eV, conductivities 1 脳 10^鈥? S cm^鈥? at 725 掳C and with some evidence of oxide ion conduction at high x values. Composition dependence of the dielectric properties shows a transition from classic ferroelectric behavior with Ba₂NdTi₂Nb₃O₁₅ to a relaxor-like behavior with Ba₂NdTi₃Nb₂O_14.5. At intermediate compositions, both a first-order phase transition and relaxor-like behavior are observed.