Temperature Dynamics of Electronic and Frequency-Impedance Spectra of Tourmaline in the Range of 300‒650 K

The paper studies the influence of tourmaline temperature on X-ray photoelectron spectra in the energy range up to 1800 eV and on the frequency dependences of impedance in the frequency range of 50 kHz–15 MHz and in the temperature range of 300‒630 K. The studies have shown that the position and width of the electron peaks of the core electrons A12p, B1s, C1s, Fe2p, Mg1s, Na1s, Fe2p, O1s, and Si2p of tourmaline weakly depend on temperature. At the same time, the concentrations of some core electrons strongly depend on the temperature of tourmaline, and their change in the temperature range of 300‒630 K is (in %): C1s 271; Na1s 175; B1s 159; and O1s 119. It has been shown that oxygen, boron, and sodium atoms significantly determine the temperature dynamics of the frequency properties of tourmaline impedance in the studied temperature range. The large difference in the tourmaline impedance modulus values, reaching up to 10%, measured upon heating from 300 to 630 K and subsequent cooling, especially in the temperature range of 300–370 K and in the frequency range of 5‒10 MHz, indicates the presence of irreversible processes on the tourmaline surface that occur during its heating and subsequent cooling. These irreversible processes may be associated with the diffusion, adsorption, and desorption of ions and ionic complexes, such as H– and OH– groups. Several relaxation regions were detected in the frequency dependences of the impedance, indicating that the charge carriers of alternating current in tourmaline crystals are free electrons and ions participating in diffusion, adsorption, and desorption. The presence of significant differences in surface impedance values upon heating and subsequent cooling of tourmaline demonstrates that tourmaline crystals can be used to create a fairly efficient thermal generator of electrical energy.