[en] Temperature dependencies of the thermally stimulated depolarization current (TSDC) and the dielectric properties at alternating current have been measured for Nd-doped KGd(WO₄)₂ crystal in the range of 250-400 K. The corresponding activation energy calculated in the range of 330-400 K is equal to 0.75±0.05 eV. Small maximum in TSDC spectrum at 330 K, characterizing by the activation energy 1.68±0.20 eV can be connected with small structural defects associated with doped Nd³⁺ ions. Reversible character of the anomaly on the temperature dependence of dielectric permittivity ε(T) at 330 K shows that the weak structure transformation of the phase transition type can take place in the crystal

[en] Main aims of Polish energy politics as well as its realization instruments are presented. The fuel base for a development of electric power industry is shortly described and assessed. The present situation of brown coal industry is discussed in detail. The information about brown coal reserves, exploited deposits, production quantities, profits etc. is given. The costs of electric power production are analysed and a raise of brown coal price is postulated. The influence of brown coal surface mining on environment is discussed and some data on the occupied areas as well as the excavations sizes are given. 6 tabs

[en] Brown coal mine ''Adamow'' is located in Central Poland and fuels power plant ''Adamow'' (600 MW). Every year 4.5-5.0 million tons of coal is extracted from 3 mines of this mine. In 1991 one of the mines ''Bogdanow'' was closed and the new one ''Kozmin'' was started. Then the problem appeared whether collect capping on external dump located 520 meters from the new mining or whether use it to fill up the closed mine located at a distance of 3700 meters. The second solution was chosen despite of the fact that was more expensive. Due to it 164 hectares of agricultural area were preserved, 116 hectares were reclaimed and water reservoir was done. The realization of this project was financed by mine and the National Fund for Environment Protection and Water Economics. 3 ills, 1 tab

[en] Pyridinium perchlorate and pyridinium fluoroborate were grown and their successive transitions were studied by means of polarized microscopic observations and measurements of linear birefringence temperature changes. The microscopic observations revealed domain structure appearance at 245 and 283.7 K for pyrimidinium perchlorate and pyridinium fluoroborate , respectively. This domain structure exists also in lower phases. Birefringence measurements confirmed two first-order phase transitions at 245.3 K and 231.5 K for pyridinium perchlorate and two continuous phase transitions at 238.7 K and 205.4 K for pyridinium fluoroborate. (author)

[en] Dielectric, dilatometric measurement and polarized microscopic observation were performed for single crystal of CsCdBr₄. These investigations showed clearly the phase transitions at 252 K, 236 K and 153 K. The jump-like change in crystal volume corresponding to the first-order phase transition was found at temperature of 236 K. Ferroelastic domain structure was observed along the a-axis below 236 K and it is presented below the transition at 153 K. Observation along the c-axis revealed new domain structure below 153 K. (author)

[en] The phase transition in RbHSeO₄ crystals of varying deuteration degree (from 0.1 to 0.9 molar fraction) is studied by using dielectric and DTA measurements as well as observations of the domain structure. It is found that crystals grown from solutions containing up to 90% deuterium show ferroelectric properties (triclinic II system). Crystals of high deuteration degree (after 4-fold crystallization from D₂O) have P2₁2₁2₁ symmetry. In crystals grown from solutions below 40% of deuterium a linear dependence of T/sub c/ on the deuterium content is observed and the extrapolation of the T/sub c/-value to completely deuterated samples gives an enhancement of about 145 K indicating the important role of proton ordering in the mechanism of phase transition. Only a slight dependence of the transition temperature for the crystals in the range of 0.5 to 0.9 molar fraction of deuterium is most probably due to the direct transition to the high temperature disordered phase which is characterised by very high electric conductivity. (author)

[en] The search of materials with efficient optically stimulated luminescence (OSL) properties and a high hydrogen content for fast neutron dosimetry has led to the development of Tl⁺-doped ammonium salts (NH₄)₂SiF₆ and (NH₄)₂BeF₄. Preliminary OSL studies have shown that the OSL in (NH₄)₂SiF₆:Tl⁺ and (NH₄)₂BeF₄:Tl⁺is efficient. In order to optimise the OSL emission and its detection, the identification of the luminescent centres in the OSL process is necessary. This study focuses on the identification of the luminescent centres associated with Tl⁺ based on optical studies in the vacuum UV (VUV) at different temperatures

[en] Phase transitions in ND₄BeF₃ crystals at T₁ = 330 and T₂ = 245 K were studied by specific heat (DSC) and X-ray lattice parameters measurements in function of temperature. These ferroelastic transitions are accompanied by anomalous heat absorption, sudden changes in the unit cell parameters and crystal symmetry. Formation of domain structure in particular phases examined under a polarizing microscope is also described. Domain walls of the type (100), (010), and (001) observable at room temperature indicate on the triclinic symmetry of the Phase II. Above T₁ the crystal becomes orthorhombic. First-order phase transition at T₂ causes the symmetry of the crystal in the Phase III to be monoclinic with the c-axis unique. The phase transition diagram is proposed and compared with the phase situation in nondeuterated NH₄BeF₃ crystals. (author)

[en] The first precise measurements of specific heat changes have been performed for a C₃N₂H₅ClO₄ crystal using an ac calorimeter. Phase transitions at about 373 and 219 K were revealed. The continuous second-order phase transition at 373 K to the ferroelectric phase is described by the Landau model using specific heat and linear birefringence data. The Landau expansion coefficients B and C are of the same order of magnitude as those obtained for hard ferroelectric materials. Thermal parameters (such as the excess enthalpy, ΔH, and the excess entropy, ΔS) of the continuous transition were estimated and discussed. During the first cooling, a distinct (∼2 K) supercooling effect was observed at the discontinuous transition at about 219 K

[en] Temperature dependences of birefringence and dielectric permittivity of [N(CH₃)₄]₂ZnCl₄ crystals in the parent phase have been studied. A supposition was made that the nonlinear character of those two dependences is caused by the presence of local spatial regions, where the motions of tetrahedral groups ZnCl₄²⁺ are correlated