Behavior of Stress-Induced Charges in Cement Containing Quartz Crystals

The recombination process of electric charges induced by stress release has been measured for cement samples embedded within quartz crystals to investigate the behavior of piezo-compensating charges in quartz-bearing rocks. The stress with a release constant τ of σ (t) = Δσ e—t/τ led to a theoretical pulse charge density q(t) = α Δσ{ερ/(τ — ερ)} (e—t/τ — e—t/ερ), where α, ε and ρ are the piezoelectric coefficient, permittivity and resistivity, respectively. The induced charges appeared on a sample measured with non-contacting electrodes depending on the number and orientation of synthetic quartz crystals, and two decay time constants of 0.25 and 2.5 s were obtained. The apparent piezoelectric coefficient for a sample with one piece of quartz was 1.0 × 10—15 C/N. However, the coefficients for samples with two pieces of quartz, which were arranged in the same or alternate directions, were 4.1 × 10—15 and 1.7 × 10—15 C/N, respectively. The behavior of piezo-compensating charges around quartz crystals in conductive cement suggests ferroelectric charge migration through the measurements of depolarization current.