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Single crystals of Mg&Ge have been obtained from melts of the constituents, and Hall effect and electrical resistivity measurements have been made from 77'K to 1000'K. Undoped crystals were n-type and had saturated impurity carrier concentration as low as 3X10" cm; silver-doped crystals were P-type and had saturated impurity carrier concentrations roughly proportional to the amount of added silver. The room-temperature Hall rnobilities were observed to be 280 cm'/volt-sec for electrons and 110 cm'/volt-sec for holes. The hole mobility observed in the extrinsic region (120 K to 350'K) of the highest purity p-type sample and the mobility difference observed in the intrinsic region (350'K to 700'K) of the n-type samples varied with temperature as T ". The mobility difference was found to decrease faster than T" above 700'K. The width of the energy gap at absolute zero, as determined from the temperature dependence of both the resistivity and the Hall effect in the intrinsic region, was 0.69~0.01 ev.

The general integral for the determination of the average resultant polarization j5 in the direction of the applied polarizing electric field is evaluated under the assumption that the spontaneous polarization vector of each crystallite is limited to a highly symmetric set of directions. With the further assumption that a ferroelectric crystal has a structure which is a slight distortion of a nonpolar structure, expressions for j5 are given which may be applied to any set of allowed polarization directions which is likely to occur; each of the 22 nonpolar crystal classes yields one such expression. The special cases of interest for each of the 10 polar classes are evaluated. A general expression for j5 as a function of electric field strength is obtained and used to determine hysteresis curves for several commonly occurring special cases. The angular distribution of polarization vectors after complete polarization is also discussed for these special cases.

Results of a thermodynamic study of the phase transitions of powdered KNO3 at two impurity concentrations (99.999% pure and 99.9% pure) are reported. Transition onset and peak temperatures have been measured between 350 and 420 K using both heat flow and photoacoustic calorimetry. The transition temperatures and characteristics observed with both techniques show excellent agreement. Specific-heat values calculated from scanning and stepped temperature heat-flow data, utilizing both positive and negative temperature increments, compare well with previously reported values. Enthalpies for the II-I, I-III, and III-II phase transitions were measured as 5.065, 2.603, and 2.084 kJ/mol, respectively, for 99.999% pure KNO3 powder using heat-flow calorimetry. The transition enthalpies and temperatures measured for 99.9% pure powder were slightly lower for all three transitions. Entropy changes for the II-I, I-III, and III-II transitions were 12.53, 6.61, and 5.30 J/mol K, respectively. Enthalpy, entropy, and Gibbs free-energy curves are presented with emphasis on the temperature range over which the ferroelectric phase transition occurs. The experimental data and calculated thermodynamic functions indicate that the ferroelectric phase III in bulk KNO3 is a metastable state at atmospheric pressure, which was not observed to exist below 350 K contrary to previous reports.

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