IFLP   13074
Unidad Ejecutora - UE
congresos y reuniones científicas
Classical to relaxor ferroelectrics to paraelectric crossovers in BaTi(1-x)Hf(x)O3
Xi´an Jiaotong University, Xi´an 7 10049, China
Conferencia; 12th International Meeting on Ferroelectricity and 18tu IEEE International Symposium on Applications of Ferroelectrics; 2009
Institución organizadora:
Xi´an Jiaotong University
Relaxors have as distinctive characteristic a broad peak in the dielectric permittivity temperature dependence that is shifted to lower temperatures as frequency decreases. It was proposed that this peak would not correspond to a transition into a long-range disordered state with microscopic polarization. Alternatively, short-range ordered polar nanoregions would appear. In some oxides with perovskite structure the charge disorder is originated either by isovalent or heterovalent cations substitution randomly distributed at B sites. In recent years the study of dielectric properties of BaTi1-xBxO3 with B = Sn, Zr and Hf have been performed. The transition from normal to relaxor ferroelectric has been observed by impedance spectroscopy. In this contribution the effect of Ti substitution by Hf in BaTiO3 for 0 ≨ x ≨ 1, to study the hyperfine interaction at B sites as function of concentration and temperature is presented. The hyperfine interaction can give information about charge distribution close to Ta probes, in this case at B sites.  Solid solutions with nominal composition x = 0.01, 0.05, 0.10, 0.30, 0.50, 0.70, 0.80, 0.85, 0.90 and 0.95 were prepared by mixing adequate quantities of high purity titanium and hafnium oxides with barium carbonate. Then the samples were obtained by the high temperature solid state reaction technique at T » 1500K and followed by X-ray diffraction characterization. Using the Rietveld procedure the lattice constants and the crystalline structures were deduced. For x > 0.2 the structures of the solid solutions are cubic. To study the hyperfine interaction at B sites the samples were thermal neutrons irradiated to produce the Ta probe thru the nuclear reaction 180Hf+n ® 181Ta. The composition and temperature dependence of the hyperfine parameters were determined by Perturbed Angular Correlation spectroscopy. From this analysis at about x » 0.30 the crossover from classical to relaxor ferroelectric is observed. A crossover from relaxor ferroelectric to paraelectric ceramic at x » 0.80 is also proposed. The dependence of local disorder with composition at B sites is observed. Charge disordered nanoregions where probes sit with lattice constant dimensions are observed. Defect regions with low concentration and random distributed oxygen vacancies close to probres cannot be omitted either.