The Role of Electronic Subsystem in the Negative Thermal Expansion of Ferroelectric–Semiconductor TlGaSe 2

Effect of illumination and external electric field on thermal expansion of TlGaSe 2 crystals has been investigated. Strong transformation of negative linear expansion coefficient has been observed. It is supposed that two main mechanisms are responsible for observed effects: formation of electret state and reverse piezoelectric effect. The electronic nature of negative linear expansion of TlGaSe 2 crystals has been proved for the first time.