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Crystal structure of Ln 3 NbO 7

Crystal structure of Ln 3 NbO 7. LnO 8. Ln in LnO 7. NbO 6. CAREER: Fundamental Structure-Dielectric Property Relationships of Fluorite Related compounds Dr. Juan C. Nino, MSE Dept., University of Florida DMR-0449710.

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Crystal structure of Ln 3 NbO 7

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  1. Crystal structure of Ln3NbO7 LnO8 Ln in LnO7 NbO6 CAREER: Fundamental Structure-Dielectric Property Relationships of Fluorite Related compoundsDr. Juan C. Nino, MSE Dept., University of FloridaDMR-0449710 This study focuses on the understanding of the origin of dielectric relaxation in the fluorite-related compounds (A2B2O7, A and B arecations), especially Ln3NbO7 (Ln3+ = La3+, Nd3+, and Gd3+). All the Ln3NbO7 compounds exhibit a dielectric relaxation. However, onlyGd3NbO7 exhibits a distinct non-centrosymmetric to centrosymmetric transition at about 70oC based on second harmonic generation (SHG) measurements. See the plot on the left. From previous measurements, it is observed that the dielectric relaxation temperature, at which the maxima of the dielectric constant occurs, matches well with the phase transition temperature. Gd3NbO7 Off-center distortion of LnO8 and NbO6 below 70oC, the dashed circles stand for the centers of polyhedra Ln O Based on the crystal structure determination and refinement, the transition is mainly due to the Nb5+ ions shifting to off-center positions within the NbO6 octahedra, as well as Ln3+ shifts to off-center positions within the LnO8 cubes, in an anti-parallel fashion. See diagram on the left. In the crystal structure of Ln3NbO7, there are three types of polyhedra: distorted LnO8 cubes, distorted NbO6 octahedra, and LnO7. Nb

  2. Lu Alex Jonathan Donald CAREER: Fundamental Structure-Dielectric Property Relationships of Fluorite Related compoundsDr. Juan C. Nino, MSE Dept., University of FloridaDMR-0449710 Education and Outreach During the last year, the main graduate student in this project, Lu Cai, has mentored two undergraduate students Alex Luis Arias and Donald Moore. After one or more semesters under Lu’s training, they both have their own projects now: Alex is working in the single crystal growth of TGS-TGSe and Don is working in dielectric/ferroelectric property measurements of oxyfluorides. To expand the awareness of science and engineering of ceramic materials as a professional field, during the summer, the NRG group has continued to be a host of the Student Science Training Program (SSTP). One high school student, Jonathan Oulton, from Daytona Beach, is participating in the group’s research and working on molten salt growth of Gd3NbO7 single crystals. International Workshop on Electroceramics, Lima, PERÚ 2008 As part of the educational and outreach component of this project, the PI organized the second in the series of International Workshops on Electroceramics across the Bolivarian countries in South America. This second workshop took place at the Universidad Nacional de Ingeniería, in Lima, Peru, from August 20-22, 2008. The local host was Professor Abel Gutarra. There were 20 presentations from researchers across Perú and one from Chile. There were 45 student participants.

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