Study of dielectric permeability and dielectric loss angle tangent of triglycine selenate depending on the conditions of growing

Triglycine selenate (TGSe) monocrystals were grown at constant temperature and constant supersaturation. Dielectric permeability and the dielectric loss (angle tangent) of TGSe were studied both in weak and in strong electric fields with growing conditions. It was stated that the Curie temperature is 22,5° ± 0,1°C. The Curie-Weiss temperature differs by 2–3,5° from the temperature corresponding to the maximum value of dielectric permeability. Nonlinearity of TGSe is determined.     

Gyrotropic properties and birefringence of Smx Tb1−xFeO3 in spin reorientation range

The polar diagrams of the Sm_xTb_1−xFeO₃ system taken for the crystallographic directions [110] and [001] have been investigated. The gyrotropic measurements data are compared to the values of the bond angles θ₁ and θ₂ calculated in terms of the lattice parameters. The correlation between the crystallographic and optical properties change as a function of composition has been obtained for the system under investigation. -The temperature measurements of the gyrotropic properties of SmFeO₃ and Sm_0.8Tb_0.2FeO₃ have shown that with temperature rising a change of shape and character of the polar diagrams takes place. The birefringence temperature dependence for Sm_0.8Tb_0.2FeO₃ in the transparency and absorption range has been determined. The results of the study show the existence of the interrelation between the crystallographic, optical and magnetic characteristics and indicate that the temperature range of spin reorientation can be reliably determined from the optical measurements.     

Atomization Energy of the Cu,Ag, Au Crystals in Terms of the Statistical Model

The statistical atom model is used for ab initio calculations of the atom binding energy in crystals. The original calculations by the above method of atomization energy at T = 0 K of the A₁ modification crystals of I^B elements group of the Periodic System are consistent with the experimental data. The atomization energy estimates of the A₂, A₃ modifications are made.     

On absorption spectra temperature dependence in lithium niobate doped with transition metal oxides

Absorption spectra temperature dependence of LiNbO₃ doped with the Cr-, Mn-, Fe, Co-, Ni- and Cu-irons is studied. Band gap variation of the doped lithium niobate against impurity, temperature and light polarization direction is determined.     

Magnetic phase transition in cubic lanthanum manganite

Studies of magnetic phase transition (ferromagnetic-paramagnetic) in cubic LaMnO₃ have been carried out. Using neutron diffraction and calorimetric investigations the temperature of this transition was determined to be equal to 148 K. The studied phase transition is close to the second order transition by nature. Transition enthalpy is estimated from the given dependence of C_p(T) and is 17 cal/mole. Linear dependence of temperature of the given magnetic transition in weak magnetic fields is established.     

Undulating membrane structure under mixed extensional-shear flow

We report on studies using a new X-ray extensional flow cell to examine, for the first time, the structure of undulating lamellar lyotropic liquid crystal systems under extensional flow. The extensional component of the flow profile produced within this cell causes the lamellae to orient. We find that, although the intermembrane spacing does not change at low flow rates, it suddenly decreases after a critical flow rate has been attained due to the stretching and straightening of the lamellae. The effects of the shear component of flow on this oriented system have been examined in the context of a theoretical model developed by Ramaswamy. Received 29 May 2001 and Received in final form 20 July 2001