Energy Loss in Nonpolar State Polycrystalline Barium Titanate

Two procedures, based on the Lissajous figure as observed on the screen of an oscilloscope, are described for the determination of electrical energy loss in dielectrics, particularly at higher temperatures. These procedures were employed to determine the losses in nonpolar state ceramic barium titanate within the temperature region 150°-550°C and over the frequency range 20 Hz50 kHz. The first procedure was used at a fixed frequency of 60 Hz and at relatively high field strengths. It was found that the loss L in microcalories per gram per cycle at fixed temperature and variable field strength E is given by the relation L = a 2 E2 + a4E4 where a 2 and a 4 are constants. At low field strengths the second term can be neglected. Coefficients a 2 and a 4 vary exponentially with the reciprocal of the Kelvin temperature. Using the second procedure at comparatively low field strengths for loss determination, interfacial polarization was observed from 200° to 400°C as shown by a sharp rise in the index e" with decrease in frequency and by an inflection in each e" versus f curve at constant temperature. It was found that the Maxwell-Wagner equation for a two-layer condenser describes the phenomenon provided that the exponent of f is 0.89 rather than unity, the concordance between calculated and observed values of e" then being quite good.