Microwave dielectric ceramics based on GdTiNb,-,.Ta,O6 and Sml _.,Y,TiTa06 have been prepared by conventional solid state
method . The GdTiTaO6 and SmTiTaO6 have aeschenite structure with positive rr and GdTiNbO6 and YTiTaO6 have euxenite
structure with negative rr. The rr of the ceramics has been tuned by preparing solid solution phases between the aeschynites and
euxenites for a possible zero rr material . It is observed that GdTiNbt_YTa.,O6 undergoes a phase transition from aeschynite to
euxenite when x=0.75 and in Sml-,YxTiTa06 for x= 0.73. The microwave dielectric properties change abruptly near the transition
region . The rr value approaches zero near the phase transition region while the samples have poor sinterability and poor quality
factor . The unloaded quality factor, dielectric constant and the sign of rr of the solid solution phases are found to depend on the
average ionic radius of the rare earth ion in RE ,-5RE',TiTaO6. The boundary of the euxenite-aeschynite phase transition occurs at
an average ( RE) ionic radius of 0.915 A in Sm,_, Y,.TiTaO6 solid solution phases
Junaid, Bushiri M; Jayasree, R S; Annamma, John; Nayar, V U(Elsevier, July 27, 2005)
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Abstract:
Polarized Raman spectral changes with respect to temperature were investigated for Pr(BrO3)3·9H2O single crystals. FTIR spectra of
hydrated and deuterated analogues were also recorded and analysed. Temperature dependent Raman spectral variation have been explained
with the help of the thermograms recorded for the crystal. Factor group analysis could propose the appearance ofBrO3 ions at sites corresponding
to C3v (4) and D3h (2). Analysis of the vibrational bands at room temperature confirms a distorted C3v symmetry for the BrO3 ion in the crystal.
From the vibrations of water molecules, hydrogen bonds of varying strengths have also been identified in the crystal. The appearance υ1 mode
of BrO3− anion at lower wavenumber region is attributed to the attachment of hydrogen atoms to the BrO3− anion. At high temperatures,
structural rearrangement is taking place for bothH2Omolecule and BrO3 ions leading to the loss ofwater molecules and structural reorientation
of bromate ions causing phase transition of the crystal at the temperature of 447 K.