Andrzej Budziak

Low temperature measurements by infrared spectroscopy in CoFe2O4 ceramic

This paper presents results of new far-infrared and middle-infrared measurements (wavenumber range of 4000–100 cm−1) of the CoFe2O4 ceramic in the temperature range from 300 K to 8 K. The band positions and their shapes remain constant across the wide temperature range. The quality of the sample was investigated by X-ray, EDS and EPMA studies. The CoFe2O4 retains the cubic structure (Fd - 3m) across the temperature range from 85 K to 360 K without any traces of distortion. Based on current knowledge the polycrystalline CoFe2O4 does not exhibit any phase transitions across the temperature range from 8 K to 300 K.

X-ray studies of the smectic B phase of the 4-bromobenzylidene-4′-alkoxyanilines

The results of X-ray studies of the nine members (4 ÷ 12) of the 4-bromobenzylidene-4′-alkyloxyaniline homologous series (nBBAA) in smectic B (SmB) and smectic A (SmA) phases are presented. Interestingly, no SmC phase was identified. The thickness of smectic layers in the SmA and SmB phases was estimated showing unexpectedly that in SmA it is bigger than in the SmB. For the SmB phase, orthorhombic unit cell parameters were determined as a function of temperature. The obtained data are discussed in relation to rotational dynamics.

Impedance spectroscopy studies of SrMnO3, BaMnO3 and Ba0.5Sr0.5MnO3 ceramics

The impedance spectrum of hexagonal SrMnO3, rhombohedral BaMnO3 and orthorhombic Ba0.5Sr0.5MnO3 ceramics, synthesized by conventional high-temperature method, was studied in a wide temperature and frequency range. The complex impedance plots of Z″ versus Z′ pointed to two contributions originating from grains and grain boundaries. The parameters of electric equivalent circuit were calculated. The semicircles related to the grain boundary are located at the lower frequency side due to higher resistivity and capacity of the grain boundaries. The Ba0.5Sr0.5MnO3 ceramics is characterized by the lowest activation energy related to the grains. The conductivities σac of all the investigated samples show plateaus being a characteristic of the dc conductivity. The conductivity of Ba0.5Sr0.5MnO3 takes the values between those of BaMnO3 and SrMnO3.