Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xx, 180 p.; also includes graphics. Includes bibliographical references (p. 139-145).

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior

SILVA, Eder Nascimento. Propriedades Vibracionais de Perovskitas Complexas Ordenadas. 2008. 181 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2008. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-05-04T19:23:25Z No. of bitstreams: 1 2008_tese_ensilva.pdf: 7886254 bytes, checksum: baaeb81edf0f9b9bff1c7ee1c5ae7c79 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-05-07T16:52:15Z (GMT) No. of bitstreams: 1 2008_tese_ensilva.pdf: 7886254 bytes, checksum: baaeb81edf0f9b9bff1c7ee1c5ae7c79 (MD5) / Made available in DSpace on 2015-05-07T16:52:15Z (GMT). No. of bitstreams: 1 2008_tese_ensilva.pdf: 7886254 bytes, checksum: baaeb81edf0f9b9bff1c7ee1c5ae7c79 (MD5) Previous issue date: 2008 / The A2B0B00O6 double perovskites can crystallize in at least 12 different space groups, where the B0O6 and B00O6 octahedra (1:1 order) alternate along the three crystallographic axis. Four perovskites with this order are studied in this work, to know: Sr2CoWO6 (I4/m), Ca2CoWO6, Ca2CoTeO6 and Sr2CoTeO6 (P21/n). In many cases, total or partial disorder due to the random distribution of the B0 and B00 cations in the B sites of the ABO3 perovskites can be observed. An example of compound with total disorder is Pb(Fe1/2Nb1/2)O3 (Cm), where the Fe3+ and Nb5+ cations possess an occupation factor 1/2 in the octahedral sites of the perovskite structure. The compounds: (i) Ba2In(In1/3U2/3)O6, Ba2In(In1/3W2/3)O6 (Fm¯ 3m), Sr2In(In1/3U2/3)O6, Sr2(In0,87W0,13)(In0,46W0,54)O6 (P21/n) and (ii) a2(Fe0,73W0,27)(Fe0,60W0,40)O6 (P21/n) and Sr2(Fe0,79W0,21)(Fe0,54W0,46)O6, Sr2(Fe0.90Te0.10)(Fe0.57Te0.43)O6 (I4/m) possess partial disorder in the sites of the B0 and/or B00 cations, but nevertheless they exhibit 1: 1 order. In the present work, the phonon spectra of the above-mentioned perovskites are studied through the Raman scattering and infrared transmittance and/or diffuse reflectance. To analyze the phonon spectra of these compounds, theory group methods are used based on three ion sub-lattices, to know: A, B0 and B00O6. The vibrational freedom degrees of the 12 ordered perovskites are described in terms of the internal vibrations of the B00O6 octahedron and of the translational modes of the A and B0 cations. This model is valid when the vibrations of the B0O6 octahedron are negligible compared with the one of the B00O6 octahedron. We used crystallographic information to discuss the processes behind the changes in the phonon energies based on the internal modes of the octahedra. Besides, our results of Raman scattering of low temperature in Pb(Fe1/2Nb1/2)O3 ceramic, reveal pronounced anomalies in the phonon spectra around N´eel temperature TN∼150 K. We attributed these anomalies to the magnetoelectric effect in this compound.