Electron paramagnetic resonance and optical spectroscopy of K3Na(CrO4)2 ferroelastics activated by MnO 4 2− molecular impurity ions

Crystals of a proper ferroelastic K₃Na(CrO₄)₂ containing molecular impurity ions MnO ₄ ^2? are studied using electron paramagnetic resonance (EPR) and optical spectroscopy. The EPR spectrum of the Mn⁶⁺ ion contained in the molecular impurity ion MnO ₄ ^2? is identified at low temperatures (T ≤ 20 K). The intensity of this spectrum decreases unusually fast as the temperature increases. A broad IR luminescence band with a vibronic structure well resolved at a temperature of 8 K is revealed. Theoretical treatment of the Mn⁶⁺ ion involved in the molecular impurity ions MnO ₄ ^2? of the K₃Na(CrO₄)₂ ferroelastic crystal suggests that an important role in this case is played by the pseudo-Jahn-Teller. The pseudo-Jahn-Teller effect offers an explanation for the appearance of a fine structure in the vibronic replicas in the luminescence spectrum, on the one hand, and accounts for the fast decrease in the intensity of the EPR spectrum of K₃Na(CrO₄)₂: MnO ₄ ^2? with increasing temperature, on the other.     

The limit state of a layer compressed by rough plates

The possibility of presenting the solution of the problem of the compression of a three-dimensional layer by two rough plates, if use is made of Prandtl's assumption of a linear variation of the shear stresses over the thickness (not depending on the coordinates along the plates), is analysed. The case of an anisotropic material with a yield point obeying Hill's condition is also considered.     

Urea (Polyurea) Greases

The review deals with greases in which organic ureas of various compositions and structures are used as thickeners. The nature of compounds participating in the synthesis of organic ureas and the main types of polyurea thickeners are considered. The physicochemical, tribological, and operation properties of plastic polyurea lubricants are discussed.     

Algorithms for Recognizing Restricted Interpolation over the Modal Logic S4

We consider the restricted interpolation property IPR in modal logics. Earlier,the decidability of IPR over the modal logic S4 was proved and a finite list was found thatcontains all logics that can possess IPR over S4. However, this list containssome undue logics. The present article gives examples of the logics.

     

Dynamic Vortex States in High-Temperature Superconductors under Pulsed Magnetization

Physics of the Solid State - A vortex system of the Bi-2212 superconductor in an external magnetic field linearly increasing at different rates has been numerically simulated using the Monte Carlo...     

On Possible States of the Crystal Structure Preceding to a Phase Transition in Zn1 – xVxSe (0.01 ≤ x ≤ 0.10) Crystals

Physics of the Solid State - The systematic new formations observed in the reciprocal lattice of the cubic structural modification of a II–VI compound are characterized using a detailed...