Effect of heat on piezoelectric properties of a ceramic element

Ceramic piezoelectric elements are affected by elevated temperatures to an extent which bears upon their use in microphones and phonograph pickups. Sensitivity and capacity measurements before and after heat tests illustrate this effect. An element, subjected to a constant temperature for one hour in the range 20°C to 100°C, suffers a permanent sensitivity loss which is negligible below 50°C and moderate (3 to 5 db) between 50°C and 80°C. Above 80°C the sensitivity loss becomes increasingly severe until at 105°C the element is essentially depolarized. Repetition of the heat treatment increases the permanent sensitivity loss, but after 3 or 4 repetitions, the loss does not increase appreciably. The element capacity is found to increase under all heat tests.