R.J. Barczyński

Electronic conductivity in Na2O-FeO-P2O5 glasses

dc and ac conductivity were studied in 50P2O5–(50−x)FeO–xNa2O and 50P2O5–(50−x)FeO–xCaO (7<x<20; in mol%) glasses. It is shown that the replacement of CaO by Na2O caused rather small increase in dc and ac conductivity. The conduction in these glasses is predominantly electronic controlled by electron hopping between Fe(II) and Fe(III) sites. Internal friction has been used to study the relaxation phenomena caused by electronic and ionic migration in sodium–iron phosphate glasses. Two peaks attributed to these processes were observed on internal friction spectra in the temperature range of 125–500 K at a frequency of about 1 Hz.

Ionic conductivity of bismuth silicate and bismuth germanate glasses

Abstract The results of d.c. and a.c. electrical conductivity measurements in Bi x Ge 1− x O 2−0.5 x (where x =0.13, 0.23, 0.33, 0.47) and Bi x Si 1− x O 2−0.5 x (where x =0.47, 0.57, 0.67) glasses are reported and analysed with the aim of understanding the conduction mechanism. A suggestion is given that the electric conductivity in these glasses can be interpreted by single ionic mechanism. An explanation of a pronounced increase in conductivity for x >0.33 was proposed on the basis of percolation in high mobility BiO 5–6 network.

The electronic conductivity mechanism in Bi-Sr-Ca-Cu-O glass-ceramics

Abstract The results of electrical conductivity measurements in Bi2O3-SrO-CaO-CuO glass-ceramics are reported. It is shown that a sharp increase in the conductivity observed at 460°C is attributed to the crystallization of the Bi2Sr2CuO6 (Bi-2201) superconducting phase in the glass matrix. The mechanism of electrical conductivity in this glass-ceramic can be explained as a result of discontinuous metallic structures of the Bi-2201 phase which appear in the glass matrix during annealing. The low-temperature conductivity obeys the law [sgrave](T) = [sgrave]0exp[(-T 0 /T)n] with n changing from 1/4 to 1/2 with decrease in the temperature. This cross-over is related to a granular structure in which a parabolic Coulomb gap exists in the density of states N(E) near E F. We also show that the superconductivity effect should be taken into account for T−1/2 conductivity behaviour. It is shown that the Bi-Sr-Ca-Cu-O glass after a very short heat treatment at 820°C exhibits the superconducting transition. In the normal state the conductivity is typical for granular metals and the activation energy continuously decreases with decreasing temperature.

Mixed ionic-polaron transport and rapid crystallization in (Bi,Pb)-Sr-Ca-Cu-O glass

Abstract The results of a.c. electrical conductivity measurements in (Bi,Pb)–Sr–Ca–Cu–O glasses were reported. Two components of total conductivity were observed. Activation energies of both processes were determined. The small polaron hopping between copper ions in a different valency state Cu I –Cu II is one process. We propose that the second is ionic conductivity caused by Cu I ions.

Internal friction in high Tc iron doped 1-2-3 yttrium ceramic superconductors

Abstract The internal friction, Youngs modulus and shielding effect in yttrium ceramics doped with various amounts of iron have been measured in the temperature range 20 – 160 K. There exist several internal friction peaks, some of them common for all specimens. Only one, around 100 K, might be inexplicitly associated with the superconducting properties. No anomaly in the internal friction has been found at the transition temperature.

Internal friction in ErBa2Cu3Ox superconductors

Abstract The internal friction ( Q −1 ) spectrum of ErBa 2 Cu 3 O x superconducting ceramics has been measured at two different frequencies (approx. 6 Hz and 250 Hz). Several subsequent cycles of simultaneous measurements of internal friction, elasticity modulus and resistivity were performed. An evolution of the internal friction during subsequent measurements and ageing in vacuum and oxygen has been observed.

Low-temperature mechanical energy dissipation phenomena in lanthanum superconductors

Abstract The anelastic properties of ceramics which belong to the lanthanum family of superconductors were studied. The internal friction and Youngs modulus measurements were carried out by the vibrating reed technique in the temperature range from 20 to 300 K. The measurement frequency was in the range of 90–760 Hz. A large internal friction, corresponding to a maximum of the relaxation, was observed at a temperature about 50–60 K. An interesting correlation of both the peak height and the relaxation strength with the dopant content x has been found. An electronic relaxation phenomenon was considered as a possible source of the low-temperature internal friction maximum. The well known HTT→LTO phase transition was observed through both a pronounced change in Youngs modulus and the internal friction maximum. Also the LTO→LTT phase transition was indirectly observed through an anomalous change in the Youngs modulus.

Anelastic effects in CuO

Abstract The anelastic effects in CuO were measured at the frequency of a few hundred Hz in temperature range 20–300 K. The samples were prepared according to the procedure known for the yttrium ceramic superconductors. The spectra show distinct similarity to those of the yttrium ceramic superconductors. The only noticeable differences are visible in the range near the superconducting transition Tc where two peaks exist in the ceramic superconductor. The outgasing of the CuO sample at temperature of 200 °C reveals the appearance of two new peaks at temperatures 130 K and 155 K. The antiferromagnetic transition at 215 K and an unknown origin phenomena at 35 K were observed which do not depend on the outgasing procedure. The results show that at least some of the properties of the cupric oxide are preserved in the yttrium ceramic superconductors.

Correlation between mechanical and electrical losses in transition metal oxide glasses

Abstract The internal friction in iron phosphate glasses containing various glass modifiers has been studied in the temperature range from 120 to 700 K. The low frequency torsion pendulum technique has been employed. The dielectric loss has been investigated by two independent methods: the absorption current method and with an a.c. transformer bridge. The internal friction spectra exhibit a low temperature peak that can be related to the electron transfer between iron atoms in different valence states. It is confirmed that the dielectric loss peak and d.c. conductivity reveal a similar activation energy to the internal friction peak. The obtained data have been interpreted in the framework of a new model of relaxation in glasses recently proposed by Hunt.

Relaxation phenomena in 1-2-3 high Tc superconductors

Measurements of internal friction and ultrasonic wave attenuation by several authors have been compared. The activation energy and relaxation time of four relaxation processes have been determined. A possible interpretation of two processes is suggested.