Phase structural transition and microwave dielectric properties in isovalently substituted La1?xLnxTiNbO6 (Ln=Ce,Sm) ceramics |
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| Affiliation: | 1. Institute for Materials Research (IMR), Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan;2. Department of Material Science and Engineering, Graduate School of Engineering, Tohoku University, Aramaki 6-6-11, Aoba-ku, Sendai 980-8579, Japan;1. School of Electronic and Information Engineering, Tianjin University, Tianjin 300072, China;2. Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072, China;1. Department of Physics, Kennesaw State University, Marietta, GA 30060, USA;2. College of Engineering, Kennesaw State University, Marietta, GA 30060, USA;3. Department of Chemistry and Biochemistry, Kennesaw State University, Kennesaw, GA 30144, USA;4. Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA;5. Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA;6. Department of Physics, SUNY Buffalo State, Buffalo, NY 14222, USA |
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| Abstract: | Aeschynite-type La1?xLnxTiNbO6 (Ln=Ce, Sm, x=0–1) ceramics were prepared via a conventional solid state method. Analysis of X-ray diffraction, Raman, infrared reflectivity spectra and the microstructures revealed a series of composition-induced phase evolution in sequence: monoclinic→coexistence of monoclinic and orthorhombic→orthorhombic structure, i.e. M→M+O→O. The critical compositions of distinguishing the dominant M or O phase were x=0.15 in La1?xCexTiNbO6 and x=0.10 in La1?xSmxTiNbO6 ceramics, exactly corresponding to the average ionic radius of rare earth ions (IR) ~1.027 Å. The crystal structure and microwave dielectric properties of RETiNbO6 (RE=rare earth) ceramics strongly depended on IR. Near-zero τf was achieved in the Ce-sample with x=0.153 (εr=28.9, Q×f=17,275 GHz@6.54 GHz) as well as in the Sm-sample with x=0.098 (εr=28.2, Q×f=19,186 GHz@6.78 GHz). Eventually, RETiNbO6 would form O euxenite (-τf), O aeschynite (+τf), and M aeschynite (-τf), as IR<0.945 Å, 0.945 Å <IR<1.027 Å, and 1.027 Å<IR<1.032 Å, respectively. The infrared reflectivity study also confirmed that the structural phonon oscillations in the infrared region dominated the dielectric performance in the microwave region for this system. |
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| Keywords: | A Sintering B X-ray methods C Dielectric properties |
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