Electrical conductivity, thermoelectrical properties, and EPR spectroscopy of copper chromite ceramic samples doped with magnesium

Abstract

The results of a study of copper chromite ceramic samples doped with magnesium are presented. The samples were synthesized according to the solid-phase method using a special procedure for preparing the initial mixture, which ensures a uniform distribution of magnesium with its content from 0.2 to 6%. The substitution of chromium for magnesium in the crystal lattice is confirmed by Raman scattering of light and EPR spectra. As the magnesium content increases from 0 to 6 at.%, the resistivity of the synthesized samples decreases by more than 3 orders of magnitude at room temperature. High thermopower values were obtained, and it was shown that the main charge carriers are holes, and the predominant mechanism of hole transport in doped samples is hopping transfer over localized states, whose density decreases with an increase in energy near the Fermi energy. It is shown that the localization radius increases with an increase in magnesium content.

Theoretical Studies of Nonlinear Relaxation Electrophysical Phenomena in Dielectrics with Ionic–Molecular Chemical Bonds in a Wide Range of Fields and Temperatures

“…Theoretical developments aimed at applying quantum kinetic theory of proton conductivity and polarization [7,[12][13][14][15][16]29,30] to questions and quantum theory of hightemperature superconductivity [43] are relevant.…”

“…→ 0, polarization goes into a quasi-stationary mode. According to the dispersion expressions (43), which are the same dispersion expressions in (38) written formally, for the diffusion type case (𝑇 <<𝑇 ) relaxation, the real and imaginary components of the dielectric constant are converted to a form corresponding to classical dipole polarization…”

“…By the method of mathematical induction in the infinite approximation of the perturbation theory at the main frequency ω, the frequency harmonic of polarization P (ω) (𝑡) ( [3], p. 16) was calculated and the nonlinear frequency-temperature spectra of the CDP were constructed and studied in detail ( [1], pp. [43][44][45][46][47][48][49]. At the same time, the polarization harmonics P ( ω) (𝑡) following P (ω) (𝑡) and multiplied by the frequency 3ω according to the methodology [1,3] can no longer be calculated.…”

“…Moreover, it is not difficult to see that built formally, on the basis of ( 50), (51), for reasons of the smallness of a parameter α = <<1 expressions ( 52), (53), in physical relation, fully satisfying the conditions of the diffusion relaxation 𝑇 < 𝑇 ; 𝑇 n,D <<𝑇 , coincide with the parameters Γ , ( ) , Γ ,D ( ) from the equalities (42). Therefore, after substitution ( 52), (53) in expressions (43), the generalized dispersion expressions can be obtained that are suitable for calculating the components of the complex dielectric permittivity (CDP) in the field of diffusion relaxation at arbitrary frequencies of a variable field according to generalized formulae (43). Then, based on the partial spectral expressions (46), approximate formulas of the linear approximation of perturbation theory (46.4) for the CDP components in the diffusion relaxation region α = <<1 , far from the critical temperature T<<T cr,relax but not at absolute zero, according to ( 52), (53), are reduced to a transcendent form…”

Effect of synthesis duration on heat and charge transport in polycrystalline CuCr1-xMgxO2

“…This mixture has been obtained by thermolysis of nitrates in a liquid phase solution in NH 4 NO 3 . Reaction and details of nitrate thermolysis are presented in [12]. According to Xray diffraction data, obtained mixtures were amorphous.…”