| Popis: |
Measurements of the complex dielectric constant of ceramic barium titanate have been made at temperatures ranging from 300°K down to 2.4°K. The frequencies employed ranged from 50 kilocycles per second up to 2 megacycles per second with the majority of the measurements at 500 kilocycles per second. The real part of the dielectric constant, K ', had a value of about 1100 at room temperature, decreasing to approximately 100 in the liquid helium temperature region (2--4°K). The slope of K' against the temperature had a high positive value of 0.01 per °K in agreement with Wul. The imaginary part of the dielectric constant, K″, had a value of about 4 at room temperature, rising to a very broad maximum of approximately 15 at 200°K and steadily decreasing below 80°K to room temperature values below 4 in the liquid helium region. The experimental work was done in the Collins cryostat of the low temperature laboratory of The Rice Institute, and the impedance measurements were made with a Boonton Q-meter and a General Radio Type 916-A impedance bridge. In addition to the pure barium titanate measurements, measurements were also made on specimens diluted with 15% and 30% strontium titanate respectively. The curves obtained for diluted specimens had the same general appearance as those for the pure barium titanate except that the sharp maximum in the K' curve, normally occurring at 390°K, was brought near room temperature in case of the 15% dilution and to 274°K for the 30% dilution. This lowering of the temperature of the peak is in accord with results reported by von Hipple, Coursey and Brand, and Jackson and Reddish. |
