Thesis (M.S.)--Ohio University, August, 2000. / Title from PDF t.p.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1973. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 132-135).

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OLIVEIRA, Glaydson Francisco Barros de. Fônons em arsenatos e molibdatos de terras-raras. 2012. 76 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2012. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-05-05T17:18:44Z No. of bitstreams: 1 2012_tese_gfboliveira.pdf: 3078993 bytes, checksum: 55955275e68814a7e33226ee36f8cd9e (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-05-07T16:52:55Z (GMT) No. of bitstreams: 1 2012_tese_gfboliveira.pdf: 3078993 bytes, checksum: 55955275e68814a7e33226ee36f8cd9e (MD5) / Made available in DSpace on 2015-05-07T16:52:55Z (GMT). No. of bitstreams: 1 2012_tese_gfboliveira.pdf: 3078993 bytes, checksum: 55955275e68814a7e33226ee36f8cd9e (MD5) Previous issue date: 2012 / The Raman spectroscopy technique was used to investigate the room-temperature phonon characteristics of two series of single crystals containing rare-earth elements: (i) the rare-eartharsenates (REAsO4), RE=Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu) and (ii) the rare-earth molybdates (RE2(MoO4)3). For the REAsO4(RE=Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu)series the Raman data were interpreted in a systematic manner based on the known tetragonal zircon structure of these compounds, and assignments and correlations were made for the observed bands. We found that the wavenumbers of the internal modes of the AsO4 tetrahedron increased with increasing atomic number. This increase seems to be correlated to the contraction of the RE–O bond length. For three out of four lattice wavenumbers observed, this tendency was not nearly so marked as in the case of the internal mode wavenumber. For the RE2(MoO4)3(RE = Sm, Eu, Gd and Tb) series the Raman spectra exhibit fewer bands than those predicted by the group theory analysis. Due to the large band overlap, correct assignment was given only to the n1 and n3 modes of the MoO4tetrahedra. We observe that the vibrations from tetrahedra II and III are degenerated. The slightly increase of the frequency of the modes n1 and n3 as RE goes from Sm to Tb is likely to be related to the contraction of the orthorhombic cell. We also recorded the Raman spectra of REGd((MoO4)3) (RE = Sm, Er and Tb). No changes were observed. However, when Mo is partially substituted by W, an extra high-frequency mode appears in the Raman spectrum. / Neste trabalho utilizamos a técnica de espectroscopia Raman para investigar as características dos fônons de duas séries de cristais contendo elementos terras-raras: (i) arsenatos de terras-rara (REAsO4) e (ii) molibdatos de terras-rara (RE(MoO4)3). Para a série REAsO4 interpretamos os resultados de modo sistemático baseado na estrutura tetragonal do tipo zircon destes compostos. Utilizamos correlações com outras publicações para fazer a designação dos modos observados. Notamos que as frequências dos modos internos do tetraedro AsO4 aumenta a medida que número atômico do elemento RE aumenta. Este aumento parece estar relacionado com a diminuição das distâncias das ligações RE – O. Entretanto, esta diminuição não foi observada de maneira marcante para os modos de baixa frequência. Para a série RE2 (MoO4)3 (RE = Sm, Eu, Gd and Tb), observamos que os espectros Raman exibem menos modos do que aqueles previstos pela análise de teoria de grupos. Devido à sobreposição das bandas, conseguimos designar com certeza apenas os modos n1 e n3 do tetraedro MoO4. Observamos que as vibrações dos tetraedros II e III são degenerados. A frequência dos modos n1e n3 aumentam ligeiramente quando o elemento RE varia de Sm até Tb, e isto deve estar relacionado com a contração da célula ortorrômbica. Também registramos os espectros Raman dos compostos REGd((MoO4)3) (RE = Sm, Er e Tb). Não foram observadas alterações significativas nos espectros Raman. No entanto, quando Mo é parcialmente substituído por W, um modo de alta freqüência adicional aparece no espectro de Raman.

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