Thin lead zirconate titanate films
The subject of study was the growth and nucleation of sol-gel deposited lead zirconate titanate (PZT) films of composition Pb(Zr0_52,Ti0_4g)O3 (PZT52/48). This particular composition is on a phase boundary between titanium-rich tetragonally structured PZT and the zirconium-rich rhombohedral phase. The coexistence and relative instability of these phases is thought to be one of the origins of high piezoelectric coefficients exhibited by films of this composition. The aims of this study were to investigate variables affecting the piezoelectric coefficients in sol-gel deposited PZT52/48 thin films. Control of preferred orientation if PZT52/48 films on platinum-coated substrates was accomplished by manipulating processing conditions, specifically pyrolysis temperature. Corona poling was investigated as an alternative to contact poling. Attempts were made to find a set of poling parameters which yielded consistent results. Piezoelectric coefficients are highly dependant on poling conditions, with coefficient being lower in insufficiently poled films or those damaged by field induced sample cracking. It was observed that (001)/(100)-oriented samples with small grains had significantly lower piezoelectric coefficients and were harder to pole than coarser-grained (00l)/(l00)- oriented samples. Samples with a more irregular grain structure and a wide distribution of grain size had the lowest piezoelectric coefficients, irrespective of preferred orientation. The impact of grain size on piezoelectric coefficients was confirmed using the FWHM of the (200) reaction. Films with more irregular grain structures had higher FWHM than those with more uniform grains and had lower d33,f and e31,f. Values of e31,f and d33f were plotted against (001) intensity a determined from xray diffraction. It was difficult to determine any correlation between piezoelectric coefficients and (001) intensity. I comparison, there was a definite inverse correlation between d33,f, e31,f and FWHM, indicating that defect concentration has much more of an impact on piezoelectric coefficients in polycrystalline thin films than (001) intensity as a result of defect-induced domain pinning.