Fine particle physics and technology; some results

Abstract

The new techniques of fine particle synthesis are shown to lead to better ceramic materials such as yttrium iron garnet (YIG) and ferroelectric lead zirconate titanate (PZT). The densities are greater than 99% of the theoretical density and the grain size can be easily controlled from 2 microns upwards. For YIG this means higher values of the nonlinear spin-wave excitation thresholdh _c. For PZT the result is higher values of the tensor componentd ₃₃ and poling voltage. It is also shown that the fine particle systems and the fine-grain microstructure lead to interesting physics results. For PZT the lowering of the peak dielectric constant, the increasing transition temperatures and the decreasing values ofd ₃₃ with decreasing grain size can be understood in terms of the changing low-frequency cut-off of the soft lattice vibration mode. Another interesting result is that for 2000 Å size particles of α-Fe₂O₃ the anisotropy constant is found to be 1·38 × 10² ergs/cm³ from Mössbauer measurements.