Deformation-induced light emission from lead zirconate-titanate (PZT)

The emission of particles and photons takes place during and after fracture of materials. The types of particles that have been observed include electrons, positive ions, neutral species in both the ground and excited states, and visible photons often called mechanoluminescence (ML). This emission can often serve as a sensitive probe of crack growth and may prove to be a useful tool for investigating molecular and microscopic events accompanying formation of cracks and details of failure modes in a variety of materials. The present paper reports that the emission of photons takes place during and after fracture of polycrystalline lead zirconate-titanate (PZT). The intensity of the photons depend strongly on the direction (relative to the direction of fracture) and magnitude of the polarization. The most emission of photons is observed when the fracture surfaces are perpendicular to the polarization direction. It is found that mechanoluminescence intensity of PZT ceramics is nearly several times more as compared to that of sucrose crystals of the same mass. The ML intensity decreases with increasing temperature of the samples and it tends to disappear at higher temperatures. It seems that the ML excitation in PZT ceramics is due to the piezo electrification. As PZT ceramics are piezoelectric, an intense electric field may be created between the two surfaces of the mobile crack. This field in turn, may be able to excite the molecules of the intervening gases. The ML intensity increases with the increasing impact velocity of the piston used to deform the sample and with mass of the samples because of the creation of more surface areas. (author)