Neutron Scattering Studies of Compositional Heterogeneity in Sol−Gel Processed Lead Zirconate Titanates

Abstract

Rietveld analyses of neutron diffraction data collected on a series of Pb(Zr 0.5 Ti 0.5 )O 3 samples, which had been prepared by sol-gel and conventional mixed oxide methods, showed that each sample contained both rhombohedral and tetragonal PZT (Pb[Zr 1-x Ti x ]O 3 ). The zirconium-to-titanium ratio in the two phases was found to be markedly different. Pair distribution functions were also calculated for some of the samples. The inability of a commonly used alkoxide-based sol-gel processing method to produce compositionally homogeneous samples is attributed to a compositional segregation that occurs early on during sol-gel processing and is not fully eliminated on high temperature heat treatment of the samples. A deliberate attempt to produce compositionally inhomogeneous materials, via the separate prehydrolysis of lead titanate and lead zirconate precursors, followed by mixing the resulting sols, was found to induce no more inhomogeneity than is present in materials prepared via the hydrolysis of precursors that were completely mixed.

Homogeneity issues in chemical solution deposition of Pb(Zr,Ti)O3 thin films

“…40 Compositional heterogeneity in sol-gel derived PZT has been detected by neutron scattering studies and attributed to segregation taking place upon early stages of processing. 42 In acetic acid-modified PZT sol the number of Zrneighbors is 0.8, noticeably less than 2.9 and 2.5 for unmodified and Acac-modified PZT, respectively. For the acetic acidmodified PZT sol, the dimeric zirconium units with bridging alkoxide groups are assumed in agreement with the structure proposed by Peter et al 43 for the Zr-propoxide in parent alcohol solution.…”

Morphotropic Phase Boundary in Ferroelectric Materials

“…However, this has never been observed and, only composition dependence studies are available in the literature. Because of the steepness of the phase boundary, any small compositional inhomogeneity leads to a region of phase coexistence (Kakegawa et al, 1995;Mishra & Pandey, 1996;Zhang et al, 1997;Wilkinson et al, 1998) that conceals the tetragonal-to-rhombohedral phase transition. The width of the coexistence region has been also connected to the particle size (Cao & Cross, 1993) and depends on the processing conditions, so a meaningful comparison of available data in this region is often not possible.…”

The monoclinic phase in PZT: New light on morphotropic phase boundaries

“…Because of the steepness of the phase boundary, any small compositional inhomogeneity leads to a region of phase coexistence (see e.g. [9,10,11,12]) that conceals the tetragonalto-rhombohedral phase transition. The width of the coexistence region has been also connected to the particle size [13] and depends on the processing conditions, so a meaningful comparison of available data in this region is often not possible.…”