  A capacitive displacement system was constructed to measure the
electric-field-induced piezoelectric strain in the simple form of either a bulk
or thin film. The system can determine an AC displacement of 2 pm precisely by
using a lock-in detection, and can measure the large displacement within a
range of $\pm$ 25 $\mu$m with a sub-nanometer resolution. The system can also
be used to measure the variation in strain within a temperature range of 210 -
450 K, allowing the evaluation of the temperature coefficient of a
piezoelectric constant and the studies on the effects of a phase transition on
the piezoelectric response. Experimental results on quartz, PZT ceramics and
thin films, and BaTiO$_3$ confirm the capabilities of the developed system.
