text: The strength of this phenomenon is maximized when the composition of a material is near the morphotropic phase bound- ary.
full_question: The strength of this phenomenon is maximized when the composition of a material is near the morphotropic phase bound- ary. The decrease in the resonant frequency of a material exhibiting this phenomenon when a mass is added to it is calculated using the Sauerbrey equation, which is the basis behind QCM instruments. This phenomenon's longitudinal coefficient is un- usually negative in PVDF. The coefficients of this phenomenon are located in a rank-3 tensor which is found in two coupled equations which relate the D-field to the stress tensor and the E-field to the strain tensor. This phenomenon occurs in ceramics that lack inversion centers, such as barium titanate and PZT. Materials exhibiting this phenomenon are used in the tips of scanning tunneling and atomic force microscopes. It famously occurs in Rochelle salt and quartz. For 10 points, name this phenomenon in which mechanical deformation of a crystal leads to the generation of an electric field, and vice versa.
first_sentence: The strength of this phenomenon is maximized when the composition of a material is near the morphotropic phase bound- ary.
raw_answer: piezoelectricity [or electrostriction]