Thermal and x-ray diffraction measurements on compositions from the system Na"K1-zNbOa h~ve revealed the presence of phase boundaries at approximately 82.5, 67.5, and 52.5. mole X ~a~b03.at 25 C, in addition to one very near the NaNbOa end member. The optimum piezoele~tnc I?roperbes. In t;hls system are apparently associated with compositions near the latter boundary. Calonmetnc dete~natlOns of t~e enthalpy and entropy changes associated with the ferroelectric-->ferroeIectric and fe~roelec~nc-->paraelectnc transformations in the system clearly revealed the presence of the phase b~undanes ~hile measureme~ts of the transformation temperatures alone did not readily reveal the boundanes. Two different superlattice perovskite phases were observed in the system, one existing in the region. ",0.98~x~0.825 and another in the region 0.825~x~0.675. No multiple-cell structures were observed In the system at NaNbOa concentrations below about 70 mole%.

Dielectric measurements and X‐ray diffraction studies were made in the system BaTiO3‐BaHfO3 for polycrystalline specimens containing from 0 to 30 mole % BaHfO3. The maximum in the dielectric constant for each composition in creased as the BaHfO3 concentration was in creased to 16 mole % and then decreased with further BaHfO3 additions. Room‐temperature lattice constants and hysteresis loops were meas ured for all compositions. A partial solid‐state phase diagram is suggested for the solid solution area of the system. The phase diagram and the dielectric behavior of the system up to 16 mole % BaHfO3 are explained on the basis of Devonshire's thermodynamic theory. The ferroelectric‐paraelectric transition in the composition containing 16 mole % BaHfO3 was essentially of second order and occurred between a ferroelectric rhombohedral phase and a paraelectric cubic phase.

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A high‐temperature X‐ray diffraction study of a high‐purity PbZrO3 specimen at 25° to 236°C is reported. The symmetry of the perovskite sub‐cell of PbZrO3 was determined unambiguously by observing the splitting of the line groups N= 12 and N= 16 when the diffraction pattern was indexed on the basis of the perovskite cell being a unit cell for the structure. Diffractometer studies were conducted of the N= 12 line group using Fe Kα radiation and of the N= 16 line group using Cu Kα radiation. The ferroelectric phase of PbZrO3 possessed a rhombohedral sub‐cell with the angle α being acute. Stable two‐phase mixtures and considerable thermal hysteresis were observed at the antiferroelectric α ferroelectric transition temperature. A very weak “extra” diffraction line was observed in the diffraction patterns of the ferroelectric and paraelectric phases, indicating that the unit cells of these structures may be multiples of the perovskite subcell.

Investigation of Rare-Earth Doped Barium Titunate 187(3) High-temperature nucleation occurred at the glassplatinum interface from 450°C. to the melting point of crystalline sodium disilicate. The maximum nucleation rate was at about 600°C.(4) Nucleation also occurred at the glass-atmosphere interface as a result of surface reaction with water vapor. Crystals were observed only aftergrowth at 800°C. and the number of crystals increased as the nucleation temperature decreased from 3i5" to 25°C. Fresh fracture surfaces were preferred sites for nucleation because of their greater surface activity. No crystals developed after exposure at these temperatures in vacuum or in dry air. The actual mechanism of the surface reaction nucleation is unknown.(5) Both alpha and beta NazSizO6 appeared as initial crystallization products. Their appearance depended on the type of nuclei that formed, which in turn depended on the nature and temperature of nuclei formation.(6) Curves of linear growth rate versus temperature were obtained for two glasses. The glass with higher impurity content had lower growth rates over the entire growth range but showed no temperature shift of the maximum point of the curve. Both O( and /3 grew metastably because both were stable with respect to the liquid; transformations between the two forms were too slow to be observed during the short growth periods used. The fact that, for a given glass, no difference in growth rates of O( and /3 was observed indicates that. factors other than relative stability were rate controlling. AcknowledgmentsGrateful acknowledgment is made to the Corning Glass Works Foundation for their financial support; William D. Scott was the recipient of a Corning Glass Works fellowship. Thanks are also extciided to Richard M. Fulrath for his basic suggestion of the microscope design and for helpful discussions during the course of the research.In this study the effect of additions of 0.0015 to 0.0030 mole fraction of rare-earth oxides on the d.-c. resistivity of sintered barium titanate was investigated. The substitution may be represented by ( & 0 3 )~ (BaTi03)1--dl, where X is the rare earth. The rare earths samarium, gadolinium, and holmium were introduced singly into the titanate, and the resistivity was measured as a function of temperature from -170" to +33OoC. An anomalous increase near the tetragonal-+ cubic transition temperature at 120°C. occurred which in some cases amounted to an increase in the resistivity of 4000 times the value in the tetragonal phase. The thermoelectric power of the material changed sign at the Curie temperature. The tetragonal phase exhibited n-type behavior whereas the cubic phase was p-type. The rhombohedra1 and orthorhombic phases exhibited conduction activation energies of the order of 0.2 e.v. whereas that in the tetragonal phase was approximately 0.1 e.v.