Structure and Properties of Ba₆₋₃ₓLn₈₊₂ₓTi₁₈O₅₄ Microwave Dielectrics.
AuthorRawn, Claudia Jeanette.
AdvisorBirnie, Dunbar P. III
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe structural investigation of Ba₆₋₃ₓLn₈₊₂ₓTi₁₈O₅₄, using the correct (doubled) unit cell, corresponding to space group Pnma (number 62), resulted in an R1 = 5.36%. The structure is made up of a network of corner sharing Ti06 octahedra creating pentagonal and rhombic (perovskite-like) channels. The pentagonal channels are fully occupied by Ba atoms, one rhombic channel is fully occupied by Sm atoms, one rhombic channel is partially occupied by Sm atoms, and one rhombic channel is shared by Ba/Sm atoms. Based on the above site occupancies, the disorders (vacancies and substitutions) were calculated for 0 < x < 0.667. Refinements in space group Pna2t (number 33) were conducted and single phase powders were examined for second harmonic signal generation to support the choice of the centrosymmetric space group Pnma. The solution of the Sm-analogue allowed for a comparison to the previously solved crystal structures of the Pr- and Nd-analogues. The crystal structure determinations of the Pr- and Ndanalogues did not take into account the superstructure reflections that doubled the unit cell and changed the space group. The changes of the dielectric characteristics E', Q, and Tf, by varying the x and/or Ln, of the solid solution Ba₆₋₃ₓLn₈₊₂ₓTi₁₈O₅₄ (Ln = La, Pr, Nd, Sm, and Eu) will be reviewed. The focus of this dissertation has been to address: 1) What structural elements cause E', Q, and Tf to change when Ln = Pr, Nd, or Sm and x is varied along the solid solution. 2) What structural elements cause E', Q, and Tf to change when x = 0.5 and Ln is varied. Previous studies established a correlation between Tf and the occurrence of octahedral tilts for the solid solution BaₓSr₁₋ₓ(Zn⅓Nb⅔)O₃ (a perovskite structure with only four-sided channels). The octahedral tilts for the Pr-, Nd-, and Sm-analogues are compared for the Ba₆₋₃ₓLn₈₊₂ₓTi₁₈O₅₄ solid solution where there are three-, four- and five-sided channels.
Degree ProgramGraduate College
Materials Science and Engineering