Piezoelectric properties have been studied on ferroelectric ceramics comprising bismuth compounds with layer structure, PbBi2Nb2O9, PbBi4Ti4O15, SrBi4Ti4O15 and Na0.5Bi4.5Ti4O15. These ceramics have the high mechanical quality factor Q(2000∼7200), low aging rate of frequency constant Nt(30∼60 ppm/time decade), low temperature coefficients both of Nt(-50 ppm/°C) and of coupling factor kt(70 ppm/°C), low Poisson's ratio σ(0.23∼0.27), and large anisotropy in coupling factor. A small value of kt in these ceramics probably relates to two-dimensional restriction on permissible rotation of the spontaneous polarization. The poling characteristics in the ceramics can be improved by some additives. Grain boundaries in these ceramics are of nearly rectangular shape, and an etch pattern of fine stripes appears always in parallel to the length of the boundary.

A piezoelectric ceramic material having low dielectric constant, high thickness coupling factor, high mechanical quality factor, high stability, and high operating temperature, has been prepared from PbTiO3 incorporated with 2.5 mol% of LaO12 and 1.0 mol% of MnO2. Typical electromechanical constants of this material are as follows: dielectric constant ε11T/ε0 230, ε33T/ε0 170; coupling factor k33 0.46, kt 0.46, k15 0.28, kp 0.07, k31 0.04; mechanical quality factor Q 1100, Poisson's ratio σE 0.20. Frequency constants Nt and N3t of the fundamental and third-harmonic thickness vibrations have temperature coefficients of −1.1 × 10−4°C−1 and −2 × 10−5°C−1, respectively. Aging rates of Nt and N3t, are +0.02% and −0.02%/time decade at 30°C, respectively. The Curie point of this material exists at 470°C, and k33 and kt increase gradually with temperature up to 400°C. This material has grain size of 2–3 μ and bending strength of 2 × 107 kg/m2, and can be polished into very thin plate. The PbTiO3 ceramics have a high potential for use in electromechanical devices at high frequency and high temperature.

PbTiO3 ceramics with high density and high resistivity have been prepared by adding less than 5 mol % of Bi2/3TiO3, PbZn1/3Nb2/3O3 or their derivatives. These ceramics have dielectric constants of about 200, and can be poled at 200°C under a d. c. field of 40 to 70 kV/cm. The piezoelectric coupling factors k 15, k 33 and k 31 amount to 0.43, 0.35 and 0.068, respectively. The value of k 33 is nearly constant up to the Curie temperature of about 500°C. The aging rate of frequency constant does not exceed 0.1%/time decade. The present ceramics can be used as stable piezoelectric elements in high temperature and high frequency.

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CdS–CdTe solar cells were prepared by epitaxial growth of CdS on p·CdTe wafers, and properties of the cells were extensively studied. The cells have a junction structure of n·CdS–(n or i)·CdTe–p·CdTe. Formation of the (n or i) layer is due to diffusion of In into CdTe; the thickness of the layer was 0.5 µm in the most efficient cell. The best cell exhibited a solar conversion efficiency of 10.5% under illumination by sunlight (AM1.3, 68 mW/cm2), and 6.0% under illumination by a simulated sunlight (AMO). The high efficiency is attributed to the reduction in both the series resistance and surface recombination, which results from the presence of the heavily doped CdS layer on the wafer. The cell is not humidity sensitive and is stable in the forward bias test, These results suggest strongly that practically useful solar cells can be manufactured from this type of junction.