Generation of Electric Field in Igneous Rocks under Non-uniform Stress

According to our previous laboratory experiments, when a block of air-dried igneous rock is placed under non-uniform stress, (1) electric currents automatically flow from the stressed volume to the unstressed volume and (2) the surface of the unstressed volume is charged positive. Because quartz-less rocks such as gabbro also generate electric signals, we can assume, not a model based on piezoelectric effect, but a model that positive charge carriers in the stressed volume are activated and diffuse into the unstressed volume. To explain these carries, we focus peroxy bonds (O3X-OO-YO3 with X, Y = Si4+, Al3+, etc.), which are one of the most ubiquitous lattice defects in igneous rock-forming minerals. When this bond is deformed under non-uniform stress, an empty energy level of the bond shifts down into the Valence band and an electron can jump in this level from an oxygen neighboring. As a result, a positive hole at the neighbor oxygen site is activated. This hole can move through the Valence band, like charge carriers in a p-type semiconductor material. In this study, based on finite element method analyses of the stress/strain distribution and measurements of thermal electromotive force, we try inspecting the model that an empty energy level shifts down into the Valence band under non-uniform stress.