The low-temperature - high-temperature rhombohedral-ferroelectric phase transition and the rhombohedral-ferroelectric - cubic-paraelectric phase transition in Nb-doped ceramics (x = 0.05 and 0.25) were investigated using dielectric and resonance frequency measurements. The dielectric behaviour in PZT(Nb)95/5 is found to obey the Curie - Weiss law above , while that of PZT(Nb)75/25 deviates from the linear Curie - Weiss law in a temperature range of above , and can be described by the relation with the exponent in the range . Dielectric dispersions are observed in the rhombohedral-ferroelectric region for both compositions. Dielectric anomalies and thermal hysteresis are observed in PZT(Nb)95/5; in contrast, no anomaly appears in PZT(Nb)75/25. Around the phase boundary region, the temperature dependences of the resonance frequencies for both compositions show remarkable anomalies. The piezoelectric constant of PZT(Nb)95/5 rapidly decreases, but that of PZT(Nb)75/25 gradually increases. These results are discussed on the basis of the coupling of M-type and R-type oxygen octahedra tilts to the polarization and strain.

T h e method of Successive Linear Approximation at Maximum Steps, described in the previous paper, has been applied to automatic lens designing on an electronic digital computer. A description is given of the form of programme used and the results of applying the method to three design problems are quoted.

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The ferroelectric PZT thin films were prepared on Pt/Ti/SiOz/Si substrate by RF sputtering method followed by the rapid thermal annealing. The preparation of the Pt and Ti thin films as bottom electrode, and their influences on the PZT thin films were studied in details. The substrate temperature during sputtering was room temperature; the rapid thermal annealing temperature was 50OoC-75O0C and the annealing time was 30-70s. The influences of different preparation parameters on the structure and electric properties were studied with X-ray diffraction technique and RT66A Standardized Ferroelectric Test System. The electric properties of the prepared PZT thin film was: P,=39pc/cm2, P,= 9.3 pc/cm2, EC=28KV/mm, ~=300, p=109 nocm.

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