W. Bak

The transport properties of polycrystalline NaNbO3 determined from immitance spectra at very low frequencies

Abstract The immitance spectroscopy method has been applied to the polycrystalline sample of NaNbO3 (NN). The very low frequency measurements (0.002–0.8 Hz) have been performed in the temperature range from 300 K to 800 K. The analysis of immitance spectra have been used to determine the ac. conductivity. The obtained data have been discussed in terms of conductivity mechanism of the sample. Some arguments are presented which indicate the important role of variable range hopping in the charge transport.

The IR properties of SbSI and SbSI:Cl ferroelectric crystal needles and μ-crystals

Abstract The diffusive-reflectance (30°) IR spectroscopy was used to explore IR-optical properties of needle-like SbSI (antimony sulphoiodide) and SbSI:Cl (chloride modified) crystals and μ-crystals (powders). It turned out to be possible to follow paraelectric-ferroelectric (PE-FE) phase transition influence on IR-spectrum as well as to observe the effect of Cl introduction into SbSI structure. Anisotropy in the water adsorption was also observed for unmodified SbSI.

Very low frequency study on transport and relaxation phenomena in LiNbO3 single crystal

Abstract The immitance spectroscopy method in very low frequency range (0.001Hz ÷ 0.8Hz) has been applied to the cleaved single crystal of LiNbO3. The results of measurements has been treated using complex plane analysis techniques. The best representation of the data in the impedance plane is obtained. The experiments performed in the temperature range 300K ÷ 950K have defined relaxation processes with the relaxation time of order 102s. Important role of variable range hopping in the charge transport have been confirmed.

Effect of Variable Valence Ion Doping on the Dielectric Properties of BaTiO3–Based Materials

Dielectric properties of BaTiO3, BaTiO3 + 0.1 wt.% Fe2O3 and BaTiO3 + 1 wt.% Fe2O3 ceramics were studied. The dielectric measurements were performed at the temperature ranging from 130 K to 500 K and at the frequency ranging from 0.1 Hz to 10 MHz. Phase transitions were also determined by a thermal analysis in a wide temperature range. Both thermal analysis and electrical characterization techniques show that the temperature of phase transition is shifted towards lower temperatures with increasing Fe2O3 content. The changes and diversity of the observed phase transition temperatures occurred as a consequence of the ion substitution. Such behaviour of the investigated polycrystalline materials may be due to the multivalence nature of the incorporated ions.

Electrical Properties of (Ba1-xNax)(Ti1-xNbx)O3 Ceramics

The (Ba1-xNax)(Ti1-xNbx)O3 (BNTNx) ceramics have been obtained from oxides by means of a conventional method. The structure and morphology of the investigated samples were characterised by an X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermal analysis of the phase transitions was performed with the use of a scanning differential calorimeter (DSC). The investigation of electrical properties of BNTNx samples at the temperature ranging from 140 K to 600 K was performed by means of dielectric spectroscopy at the frequency ranging from 0.01 Hz to 10 MHz. An analysis of the temperature dependences of complex dielectric permittivity provided new details about the specific features of physical properties of the ceramic samples.

Study of the Phase Transition in Polycrystalline Ba(Ti0.90Sn0.10)O3

The results of X-ray, dilatometric and dielectric measurements of the Ba(Ti0.90Sn0.10)O3, (BTS10) polycrystalline sample are presented. A cubic symmetry at room temperature (Tr) was determined. The dielectric measurements showed the influence of Sn addition on the character of the phase transition in the BaTiO3 structure. A diffuse phase transition (DPT) for BTS10 was found. In the paraelectric phase the change of the γ parameter at Burns temperature (TB) takes place. This temperature corresponds to the glass temperature (Tg), which was observed by dilatometric measurements.

Influence of Sn-Substitution on the Phase Transitions Character in Polycrystalline (Ba0.90Sr0.10)(Ti1-ySny)O3

The X-ray, microstructural and dielectric investigations of the (Ba0.90Sr0.10)(Ti1-ySny)O3 (0 ≤ y ≤ 0.25) polycrystalline solid solutions were performed. The dielectric measurements showed changes of physical properties and the character of the paraelectric - ferroelectric (PE-FE) phase transition with the increase of a tin concentration. The obtained results suggest the occurrence of polar regions in a wide temperature range. The increase of the tin concentration to y = 0.25 leads to the freezing of a cubic phase, which is typical for relaxor ferroelectrics.

Influence of Sr and Zr Substitution on Dielectric Properties of (Ba1-xSrx)(Ti1-xZrx)O3

Polycrystalline samples (Ba1-xSrx)(Ti1-xZrx)O3 for x = 0.01, 0.05 and 0.10 (abbreviated to BSTZ1, BSTZ5 and BSTZ10) were obtained by means of a conventional ceramic technology. The EDS and EPMA measurements revealed that the samples were perfectly sintered, chemically homogeneous and confirmed their high quality. The DSC and dielectric measurements showed that the addition of strontium and zirconium to BaTiO3 (BT) changed the nature of phase transitions. For BT and BSTZ5 three sharp phase transitions were observed, whereas for BSTZ10 sample a diffuse phase transition occurred.

TrP140: Polaronic transport in LiNbO3 at elevated temperatures

Abstract The ac electrical response of cleaved undoped LiNbO3 single crystal in very low frequency range (0.001Hz ÷ O. 8Hz) has been analyzed as a function of temperature (300K ÷ 950K) using complex plane analysis techniques. The complex admittance has been used to identify relaxation processes within the crystal. Measurements of the thermoelectric power and dc conductivity have been carried out in the temperature range from 430K to 950K. Obtained results allowed to determine the order of magnitude of charge carrier mobility and their concentration as well as the type and mechanism of electric conduction. Arguments are presented which indicate polaronic transport in LiNbO3 up to about 600K.

Study of Physical Properties of Ba(Ti1−2xFexNbx)O3 Ceramics

Ba(Ti1-2xFexNbx)O3 (abbreviated to BTFNx) solid solutions were prepared by a conventional solid state reaction method. The results of the structural, microstructural, dielectric and Mossbauer investigations of the polycrystalline samples with x = 0, 0.05, 0.10 and 0.33 are presented. The EDS studies revealed that the samples were well sintered and that the material was chemically homogeneous. The transformation from the normal to the relaxor ferroelectric state with the increase of Fe and Nb ions content was observed.