Structure-property relationships in zirconium tin titanate microwave dielectrics.

摘要

Zirconium tin titanate ceramics were investigated for structure and dielectric properties. Dielectrics of composition Zr{dollar}sb{lcub}x{rcub}{dollar}Sn{dollar}sb{lcub}y{rcub}{dollar}Ti{dollar}sb{lcub}z{rcub}{dollar} (x + y + z = 2) possess low dielectric loss and adjustable temperature coefficient at microwave frequencies. Stable composition Zr{dollar}sb{lcub}0.8{rcub}{dollar}Sn{dollar}sb{lcub}0.2{rcub}{dollar}TiO{dollar}sb4{dollar} was investigated to obtain structural information. The effects of sintering aids on microstructure and dielectric properties of Zr{dollar}sb{lcub}0.8{rcub}{dollar}Sn{dollar}sb{lcub}0.2{rcub}{dollar}TiO{dollar}sb4{dollar} were studied. A relatively new technique of microwave dielectric characterization utilizing infrared reflectance data was also examined.; The crystal structure of Zr{dollar}sb{lcub}0.8{rcub}{dollar}Sn{dollar}sb{lcub}0.2{rcub}{dollar}TiO{dollar}sb4{dollar} was investigated with the neutron powder diffraction and Rietveld refinement method. The Zr{dollar}sb{lcub}0.8{rcub}{dollar}Sn{dollar}sb{lcub}0.2{rcub}{dollar}TiO{dollar}sb4{dollar} possesses the {dollar}alpha{dollar}-PbO{dollar}sb2{dollar} type structure. The extended X-ray absorption fine structure (EXAFS) spectroscopy around Zr-ion reveals that zirconium is in 8-fold coordination as in Zr{dollar}sb5{dollar}Ti{dollar}sb7{dollar}O{dollar}sb{lcub}24{rcub}{dollar}. The tin has six oxygens surrounding it. The X-ray diffraction and EXAFS results indicate that Zr{dollar}sb{lcub}0.8{rcub}{dollar}Sn{dollar}sb{lcub}0.2{rcub}{dollar}TiO{dollar}sb4{dollar} exists in a structural state between that of high temperature ZrTiO{dollar}sb4{dollar} and Zr{dollar}sb5{dollar}Ti{dollar}sb7{dollar}O{dollar}sb{lcub}24{rcub}{dollar}. Consistent with the EXAFS results, a Raman spectral analysis concludes that tin ions prefer to be on titanium sites. A superstructure was observed in Zr{dollar}sb{lcub}0.8{rcub}{dollar}Sn{dollar}sb{lcub}0.2{rcub}{dollar}TiO{dollar}sb4{dollar} most probably caused by the non-stoichiometric nature of the sample.; The combined sintering-aids ZnO and La{dollar}sb2{dollar}O{dollar}sb3{dollar} act as grain growth enhancer in Zr{dollar}sb{lcub}0.8{rcub}{dollar}Sn{dollar}sb{lcub}0.2{rcub}{dollar}TiO{dollar}sb4{dollar} ceramics. Low level doping with ZnO and La{dollar}sb2{dollar}O{dollar}sb3{dollar} (up to 0.30 wt%) is good for densification and dielectric properties. These additives do not affect the dielectric constant and temperature coefficient. Dielectric losses increase significantly at additive levels higher than 0.15 wt%. Prolonged sintering reduces dielectric losses. With 0.15 wt% additives, a ceramic having dielectric constant, quality factor and temperature coefficient of frequency at 4.2 GHz, of 37.6, 12800 and {dollar}-{dollar}2.9 ppm/{dollar}spcirc{dollar}C, respectively was obtained.; The lattice vibrations of zirconium tin titanate were investigated using infrared spectrophotometer. Microwave dielectric functions were determined by the Kramers-Kronig analysis followed by the classical dispersion analysis of the infrared reflection spectra. The relative tendency of the spectroscopically determined dielectric functions is in good agreement with those directly measured. The loss tangents are underestimated by this technique. This technique is not sensitive to small variations in the impurity level. For comparative studies or for the development of new materials, this method is promising.