The electrical conductivity of NaNO3–xAl2O3 composites has been studied over the wide range of temperature and frequency by means of impedance spectroscopy. The real part of the frequency dependent conductivity exhibits a simple power law feature and the dimensionless frequency exponent n has been determined. The conductivity spectra show scaling behaviour when the conductivity spectra are scaled by σdcT, where T is temperature in Kelvin. The real part of dielectric permittivity shows saturation at higher frequencies and a strong dispersion at lower frequencies. The imaginary part of permittivity varies inversely with frequency, due to the presence of dc conductivity. The frequency dependent plots of M″ and Z″ show that the conductivity relaxation is non-Debye in nature. The Kohlrausch-Williams-Watts stretched exponential function was used to describe the modulus spectra and the stretching exponent β is found to be temperature independent. The conductivity relaxation time has been estimated from the modulus spectra. The activation energy responsible for relaxation has been evaluated and it was found to be almost same as that of dc conductivity.

ac Conductivity analysis and dielectric relaxation behaviour of NaNO3–Al2O3 composites

The electrical conductivity of some nickel-zinc ferrites is studied as a function of temperature. The ferrites with iron in excess show n-type conduction and those with iron in deficiency show p-type conduction. Seebeck coefficient, X-ray analysis, and saturation magnetisation are also carried out to discuss the conductivity of these ferrites.



Es wird die elektrische Leitfahigkeit einiger Nickel-Zinkferrite als Funktion der Temperatur gemessen. Ferrite mit Eisenuberschus zeigen n-Leitfahigkeit, solche mit Eisenmangel p-Leitfahigkeit. Untersuchungen des Seebeckkoeffizienten, der Sattigungsmagnetisierung sowie Rontgenanlysis werden durchgefuhrt, um die Leitfahigkeit dieser Ferrite zu diskutieren.

Electrical conductivity of some nickel‐zinc ferrites

The electrical conductivity and thermoelectric power of some lithium–titanium ferrites with small amounts of manganese and zinc have been studied as a function of temperature in the range of 300–550 K and are reported here. The conductivity variation shows two different regions with a large variation in the activation energies. The possible mechanisms with respect to ionic conduction and electron hopping are discussed with the support of thermoelectric power measurements. Lattice parameters are also calculated from x‐ray diffractograms for confirming the single‐phase nature of the ferrites.

Electrical conductivity and thermoelectric power measurements of some lithium–titanium ferrites

AC conductivity, dielectric constant, loss and electric modulus of Sodium nitrate system have been studied in the frequency range from 1Hz to 10MHz and in the temperature range from 303 K to 563 K by employing impedance spectroscopy. The frequency dependent ac conductivity follows Jonscher’s universal power law. Dimensionless frequency exponent (n), dispersion parameter (A) are determined. The change over frequency independent conductivity to frequency dependent conductivity at all temperatures shows the relaxation mechanism. The variation of real part of dielectric constant with frequency shows strong dispersion at low frequencies and saturation at high frequencies. The presence of peaks in the frequency plots of dielectric loss, imaginary parts of impedance and modulus are attributed to the relaxation processes. It is also confirmed by the temperature dependence study of real part of dielectric constant. The activation energy from relaxation processes and conductivity has been evaluated.

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Dielectric Relaxation, Ionic Conduction and Complex Impedance Studies on NaNo3 Fast Ion Conductor

Enhanced ionic conduction in NaNO3 by dispersed oxide inclusions

The anisotropy of electrical conduction in single crystals of sodium nitrate which belongs to the trigonal system is studied and the non-vanishing coefficients of the conductivity tensor are $\sigma\_{11}$ = $\sigma\_{22}$ = 7.08 x 10$^{-10}\Omega^{-1}$ cm$^{-1}$ and $\sigma\_{33}$ = 1.32 x 10$^{-9}\Omega^{-1}$ cm$^{-1}$ at 200 $^\circ$C. The dependence of electrical conductivity on temperature can be represented by the expression $\sigma = 2.98\exp (- 10930/T) + 4.16 x 10^{12} \exp (-25280/T)\Omega^{-1} cm^{-1}$, and can be approximated to two straight lines on the plot of log $\sigma$ against I/T. These are interpreted as impurity influenced and intrinsic regions. Based on the experimental result that the conductivity decreased with the addition of divalent positive ion impurities, the mechanism of electrical transport is inferred to be via interstitial positive ion jumps with a jump activation energy of 0.94 eV. From the straight line for higher temperatures, the formation energy of Frenkel defect pair is deduced to be 2.46 eV. Effects of association of impurities with corresponding charge compensating point defects are discussed and a value of 0.5 eV appears to be reasonable for the association energy of the divalent positive ion impurity-positive ion vacancy complex. The divalent negative ion impurity-positive ion interstitial complex appears to be practically dissociated at room temperature. In the structure sensitive region, the positive ion interstitials that are responsible for the electrical transport appear to arise mostly as charge compensators for divalent negative ion impurities like SO$^{2-}\_4$.

Electrical Conduction in Sodium Nitrate Cyrstals

The electrical conductivity, σ of single crystals of sodium chlorate (m.p. 256 °C) grown from solution is studied in the temperature range 100 to 250 °C. A plot of lg ( σT ) against 1000/ T gives a fairly continuous curve. It is resolved into three straight lines by a special graphical procedure. The experimental data can then be represented by σT = 2 x 10 -4 e -6376/ T + 8 x 10 9 e -19012/ T +10 29 e -41386/ T . The addition of the divalent cationic impurity Ba 2+ increased the conductivity between 130 and 80 °C, indicating a cation vacancy jump mechanism. The activation energy for the migration of cations is estimated to be 0.55 ± 0.02 eV and the energy of formation of thermal defects to be 2.18 eV. The conductivity changes are discussed in relation to the enhanced optical absorption coefficient in the long wavelength fundamental region and also in relation to the anomalous thermal expansion and dielectric constant of the crystal at the higher temperatures. Above 200 °C the conductivity increases at a higher rate. Several causes were considered and the effect is most probably due to products of thermal decomposition.

Electrical Conductivity in Sodium Chlorate Crystals

D.c. electrical conductivity of single crystals of NaClO$\_{3}$ with varying concentrations of divalent cation impurity are studied. The low-temperature conductivity data are analysed to obtain the association energy between the divalent cation impurity and the cation vacancy. By a suitable analysis developed for the extrinsic and intrinsic overlapping region the formation energy per defect pair has been determined. Almost all the defect parameters are determined by graphical treatment of the conductivity data. Finally these parameters are refined by a least square fit of the conductivity data. The values of the various parameters obtained are: (1) impurity-vacancy association energy E$\_{\text{a}}$ = 0.22 $\pm $ 0.01 eV. (2) jump activation energy of cation vacancy E$\_{\text{lj}}$ = 0.46 $\pm $ 0.01 eV. (3) pre exponential factor for vacancy mobility $\mu \_{01}$ = 0.004 cm$^{2}$ V$^{-1}$ s$^{-1}$. (4) jump activation energy of interstitial cation E$\_{\text{2j}}$ = 0.85 $\pm $ 0.04 eV. (5) pre-exponential factor for interstitial mobility $\mu $$\_{02}$ = 14.7 $\text{cm}^{2}$ $\text{V}^{-1}$ $\text{s}^{-1}$. (6) formation energy of a Frenkel defect pair E$\_{\text{f}}$ = 1.98 $\pm $ 0.02 eV. (7) entropy of formation of a Frenkel defect pair s$\_{\text{f}}$ = 3.0 $\times $ 10$^{-3}$ eV K$^{-1}$.

C. Ramasastry

Papers

Electrical Conduction in Sodium Nitrate Cyrstals

Electrical Conductivity in Sodium Chlorate Crystals

Point Defects in Sodium Chlorate Crystals