Electrical conductivity of the ferroelectric sodium vanadate,potassium vanadate,lithium vanadate and their solid solutions

The d.c. electrical conductivity of sodium vanadate, potassium vanadate, lithium vanadate and their solid solutions sodium-potassium vanadate, sodium-lithium vanadate were measured by a two-probe method in the temperature range covering their transition points. These materials show sharp change in conductivity at their phase transition temperatures. In sodium, potassium and lithium vanadates an exponential increase in d.c. conductivity is observed in ferroelectric region while discontinuities are observed above the transition temperatures. The activation energy in paraelectric state of the solid solutions is found to be higher than in ferroelectric state. In solid solutions the activation energy depends upon sodium vanadate concentration.     

Lanthanum oxide doping effect on dc electrical conductivity of ferroelectrics sodium vanadate and rubidium vanadate

The temperature dependence of dc electrical conductivity was measured by two-probe technique in the vicinity of phase transition point for ferroelectrics sodium vanadate and rubidium vanadate doped with different concentrations of La₂O₃. These materials show a sharp change in conductivity at their phase transition temperatures. The results were found to obey the conventional exponential law and the activation energies were calculated for ferroelectric and paraelectric states. It was found that activation energy in ferroelectric phase is smaller than in the paraelectric phase. The activation energy increases slowly with increase in doping concentration of La₂O₃ up to 0·1 mol%, however, it decreases with further increase in doping concentration, in both ferro and para states. The dc electrical conductivity below the Curie temperature is of mixed type (ionic-electronic) while it is electronic type above the Curie temperature.     

Studies on dielectric hysteresis of ferroelectric sodium vanadate,rubidium vanadate,cesium vanadate and their solid solutions

The dielectric hysteresis property of sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions has been studied in the temperature range covering their transition points. The hysteresis loop method is used for coercive field measurements. It was observed that the coercive field decreases with increasing temperature, and that it also decreases with increasing sodium concentration in the solid solutions (sodium-rubidium) vanadate and (sodium-cesium) vanadate.     

Thermoelectric power of ferroelectric potassium vanadate,cesium vanadate,lithium vanadate and their solid solutions

The thermoelectric power of the vanadates of potassium, cesium and lithium and their solid solutions was measured in the temperature range covering their transition points. The thermoelectric power measurement was carried out by the two-electrode technique for pellets of polycrystalline ceramic samples. The thermoelectric power increased with temperature initially, then decreased attaining a zero value at the transition temperature. As the concentration of KVO₃ increased the thermoelectric power decreased for the solid solutions (K _x − Cs_1−x )VO₃, whereas the thermoelectric power increased with increase in concentration of KVO₃ for the solid solutions (K _x − Li_1−x )VO₃. Vanadates of potassium, cesium, and lithium and their solid solutions showedP type semiconductor behaviour in ferroelectric state andn type semiconductor behaviour in paraelectric region.     

Dielectric hysteresis of undoped and dysprosium doped ferroelectric potassium vanadate

Dielectric hysteresis properties of undoped and dysprosium-doped potassium vanadate have been studied in the temperature range covering their transition points. The coercive field of these materials was measured by the hysteresis loop method. It is observed that the coercive field of KVO₃ doped with Dy₂O₃ at different concentrations (0 to 3 mol%) is remarkably dependent on doping concentration. It is also seen that undoped KVO₃ shows ferroelectric behaviour up to 320°C while Dy₂O₃-doped KVO₃ samples show ferroelectric behaviour up to 380°C for all concentrations.     

Studies on dielectric hysteresis of ferroelectric potassium vanadate and lithium vanadate doped with Gd2O3

The dielectric hysteresis property of undoped and Gd₂O₃-doped potassium vanadate and lithium vanadate has been investigated in the temperature range covering their transition points. The hysteresis loop method has been used for coercive field measurements. The coercive field of Gd₂O₃-doped KVO₃ and LiVO₃ increases for 0·025, 0·05, and 0·1 mol %, however, it decreases for 0·5, 1 and 3 mol % of Gd₂O₃. It was found that the Curie temperatures of KVO₃ and LiVO₃ remain the same for various concentrations of Gd₂O₃.     

Pyroelectric properties of ferroelectric potassium-cesium vanadate and potassium-lithium vanadate

Measurements of pyroelectric currents and coefficients of poled sintered discs of ferroelectric solid solutions, potassium-cesium vanadate and potassium-lithium vanadate have been investigated in the temperature range covering their transition points. In these solid solutions, K _x Cs_1−x VO₃ and K _x Li_1−x VO₃, pronounced peaks have been observed at the ferroelectric curie temperatures. The peak values of pyroelectric currents and coefficients change with change in potassium concentration in both the solid solutions.     

Electrical conduction of sodium acetylacetonate

The temperature dependence of DC electrical conductivityσ of sodium acetylacetonate compound Na(ac,ac) is studied for fresh and polarized samples. Both samples show semiconductor behaviour, but the value ofσ for the fresh sample is higher than that of the polarized sample. Three distinct regions are observed in the temperature conductivity curves. The conduction mechanism of each region is discussed. Anomalous conductivity phenomena are observed above 105°C and attributed to unidirectional intermolecular or phase transformation. The results are discussed on the basis of ionic conduction and some conduction parameters such as conduction energyE _c, transport energyE _u, ion mobilityu, free ion densityn, are calculated.     

Electrical conductivity measurements on gel grown KDP crystals added with urea and thiourea

Pure and impurity added (with urea and thiourea) KDP single crystals were grown by the gel method using silica gels. Electrical conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 30 to 140‡ C by the conventional two-probe method. The present study shows that the conductivity in KDP crystals, for both the impurities considered, increases with the increase in impurity concentration and temperature. Activation energies were also determined and reported.     

]Electrical conductivity measurements on gel grown KDP crystals added with some ammonium compounds

Pure and impurity added [with NH₄CI, NH₄NO₃, NH4₄H₂PO₄, (NH₄)₂CO₃ and (NH₄)₂SO₄] KDP single crystals were grown by the gel method using silica gels. Electrical conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 28 to 140°C by the conventional two-probe method. The present study shows that the conductivity in KDP crystals, for all the five dopants considered, increases with the increase in impurity concentration and temperature. Activation energies were also determined and reported.     

Electrical conductivity of metastable κ-CeZrO4 phase possessing ordered arrangement of Ce and Zr ions

Electrical conductivity σ_t of metastable κ-CeZrO₄ possessing ordered arrangement of Ce and Zr ions in a manner similar to a pyrochlore-type was measured as a function of temperature and time, and compared with tetragonal metastable t′-(Ce_0.5Zr_0.5)O₂ and t′_meta-(Ce_0.5Zr_0.5)O₂ phases possessing random arrangement of the cations. The κ disk was prepared by reoxidizing a pyrochlore-type precursor in O₂ gas at 873 K. The σ_t as measured for the κ-CeZrO₄ was reproducible as a function of temperatures between 957 and 1190 K. At increasing temperatures above 1233 K, the σ_t decreased gradually with time due to the phase transition: κ → t′, and became consistent with the t′. Although the κ-CeZrO₄ phase is thermodynamically less stable than the t′-(Ce_0.5Zr_0.5)O₂, it was virtually stable up to around 1233 K. It was found from the change in the σ_t due to the phase transition that the σt(Ce_0.5Zr_0.5)O₂ for the metastable κ-CeZrO₄ was an order of magnitude higher than that for the t′ and was similar to that for the σt_meta. It was previously reported that a phase transition, t′ → t′, occurred above 1143 K. The phase transition, κ → t′, accompanied by redistribution of the cations appeared to occur at higher temperatures than that for t′_meta → t′ leaving random cation arrangement.     

Uncoupled, asymptotic mode III and mode E crack tip solutions in non-linear ferroelectric materials

Complete asymptotic solutions for the mode III, longitudinal or anti-plane shear, and mode E applied electric field with conducting or insulating crack cases are presented for idealized ferroelectric switching materials. The mathematical procedure required to solve these problems has been presented by Rice (J. Appl. Mech. 34 (1967) 287). The constitutive behavior of the material is specified by an initial linear response, a segment of non-hardening switching behavior, i.e. perfect plasticity in the mechanical case, and finally a region where lock-up occurs. The crack tip solution is characterized by an outer solution with a standard r^−1/2 singularity that is not centered on the crack tip, a switching zone with the solution given by a simple radial slip line field, and an inner lock-up region which surrounds the crack tip.     

Dielectric and pyroelectric properties of sintered discs of sodium meta vanadate

The dielectric and pyroelectric properties of poled and unpoled sintered discs of sodium meta vanadate were investigated in the temperature range from room temperature to 450°C. Dielectric constant and loss tangent anomalies were found around 375–390°C, while in pyroelectric coefficient, two anomalies were noticed at 250±25°C and 360±50°C respectively.     

Electrical studies on ceramic samples of Rb2Ti4O9, Rb2Ti5O11 and RbKTi4O9

Electrical conductivity studies have been reported on Rb₂Ti₄O₉, Rb₂Ti₅O₁₁ and RbKTi₄O₉ in the temperature range 373 K to 750 K. Three distinct regions have been identified in the log(σT) versus 1000/T plots, the lowest temperature region being attributed to extrinsic defects, the intermediate one to exchange of alkali ions and the highest temperature region to thermally created defects. A phase transition is indicated for each of the three compounds. The plot of resistivity with temperature further indicates the occurrence of a positive temperature coefficient of resistivity in RbKTi₄O₉.     

Electrical second harmonic generation and temperature autostabilized nonlinear dielectric element in ferroelectric solid solutions (Na x K1−x )VO3 and (Na x Li1−x )VO3

Second harmonic generation and temperature autostabilized nonlinear dielectric element (TANDEL) effect have been studied for ferroelectric solid solutions (Na _x K_1−x )VO₃ and (Na _x Li_1−x )VO₃ in the vicinity of the Curie temperature. The generated second harmonic is linear for low biasing d.c. fields with zero off-set. The deviations from linear behaviour and a sharp decrease in the amplitude of second harmonic is observed at higher d.c. bias voltages. The TANDEL elements, in the autostabilized state, adjust their impedance against the variation of applied a.c. voltage. The observed zero off-set might be due to the presence of defects which give internal bias and generate second harmonic.     

Determination of solubility products of phosphate and vanadate apatites of calcium and their solid solutions

To understand the toxic effects of vanadium on the human skeletal system, the solubility products of phosphate and vanadate apatites of calcium and eight of their solid solutions, spread over the entire compositional range, were investigated at 37° C in 0.165 M sodium chloride solution. They were found to increase with increase in the vanadium content, the dissolution being found to be stoichiometric. A theoretical interpretation based on changes in lattice and hydration energies resulting from isomorphous ionic substitution is advanced.     

Electrical conductivity of metastable κ-CeZrO4 phase possessing ordered arrangement of Ce and Zr ions

Electrical conductivity σ_t of metastable κ-CeZrO₄ possessing ordered arrangement of Ce and Zr ions in a manner similar to a pyrochlore-type was measured as a function of temperature and time, and compared with tetragonal metastable t′-(Ce_0.5Zr_0.5)O₂ and t′_meta-(Ce_0.5Zr_0.5)O₂ phases possessing random arrangement of the cations. The κ disk was prepared by reoxidizing a pyrochlore-type precursor in O₂ gas at 873 K. The σ_t as measured for the κ-CeZrO₄ was reproducible as a function of temperatures between 957 and 1190 K. At increasing temperatures above 1233 K, the σ_t decreased gradually with time due to the phase transition: κ→t′, and became consistent with the t′. Although the κ-CeZrO₄ phase is thermodynamically less stable than the t′-(Ce_0.5Zr_0.5)O₂, it was virtually stable up to around 1233 K. It was found from the change in the σ_t due to the phase transition that the σ_t for the metastable κ-CeZrO₄ was an order of magnitude higher than that for the t′ and was similar to that for the t′_meta. It was previously reported that a phase transition, t′_meta→t′, occurred above 1143 K. The phase transition, κ→t′, accompanied by redistribution of the cations appeared to occur at higher temperatures than that for t′_meta→t′ leaving random cation arrangement.     

Study of non-isothermal kinetics, electrical and optical properties of (GaSeTe) films

Ternary Ga_xSe_86−xTe₁₄ amorphous films (x=15 and 36) were prepared by thermal evaporation. The results of differential scanning calorimetry (DSC) at different heating rates are reported and discussed. The glass transition activation energy, E_t, and the crystallization activation energy, E_c, were evaluated by measuring the heating rate dependence of the glass transition, crystallization onset and peak crystallization temperatures. The average calculated values of E_t and E_c are 140.29 and 97.89 kJ/mol, respectively. The electrical conductivity of amorphous Ga_xSe_86−xTe₁₄ thin films with different thickness has been measured in the temperature range (263.2-333.3 K) and this allows the effect of introducing a metallic impurity to be observed. It was observed that conductivity increases with increasing activation energy and with a lowering of the pre-exponential factor, which suggests the results can be explained in terms of hopping conduction. The optical constants of these films were determined by transmission and reflection measurements at normal incidence in the spectral range of 500-800 nm. The refractive index has anomalous behavior in the spectral range 400-500 nm. The refractive index dispersion can be fitted to a single oscillator model.     

Electrical conductivity and dielectric measurements of CoMTPP

Results of X-ray diffraction patterns (XRD) show that the powder of 5,10, 15,20-Tetrakis(4-methoxyphenyl)-21H,23H-porphine cobalt(II) (CoMTPP) has polycrystalline nature with triclinic structure. Miller's indices, (hkl), values for each diffraction peak in XRD spectrum are calculated. The electrical conductivity and dielectric properties of bulk CoMTPP have been investigated in the frequency range 42 Hz–5 MHz and in the temperature range 298–413 K. The frequency dependence of electrical conductivity, σ (ω, Τ), follows the Jonscher's universal dynamic law. The obtained results have been discussed in terms of the correlated barrier hopping (CBH) model, which is well adapted to CoMTPP semiconductor material. Complex impedance data are obtained at different frequency and temperature. The best fitting for the Cole–Cole plots can be represented by an equivalent circuit element composed of RQC. The conductivity in the direct regime, σ_dc, is described by the variable range hopping (VRH). The values of dielectric constant, ?^′ (ω), and dielectric loss, ?″ (ω), are found to be decrease with increasing frequency due to the interface states capacitance.     

Thermal conductivity and thermal expansion of stainless steels D9 and HT9

Renewed interest in the use of metallic fuel in a liquid-metal fast breeder reactor has prompted study of the thermodynamic and transport properties of fuel and cladding materials. Two stainless steels are of particular interest because of their good performance under irradiation. These are D9, an austenitic steel, and HT9, a ferritic steel. Thermal conductivity and thermal expansion data for these cladding alloys are of particular interest in assessing in-reactor behavior. These two properties were measured for the two steels at temperatures to 1200 K. Of particular interest is the influence on these properties of a phase transition in HT9.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.