Long-Lived Induction Signal in Yttrium Iron Garnet

JETP Letters - The results of the experiments on an yttrium iron garnet film have been reported, demonstrating two types of long-lived free induction signals. The first type corresponds well to...     

Transformation of dielectric properties and appearance of relaxation behavior in Pb<Subscript>5</Subscript>(Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>x</Subscript>)<Subscript>3</Subscript>O<Subscript>11</Subscript> crystals

The special features of the dielectric properties and conduction of ferroelectric crystals of Pb₅(Ge_1?xSi_x)₃O₁₁ (0 ≤ x ≤ 0.67) solid solutions were studied. Permittivity anomalies close to the temperatures T₁ ≈ 260 K and T₂ ≈ 130 K, the appearance of relaxator behavior at x > 0.35, and critical behavior of the concentration dependences of dielectric and pyroelectric characteristics at x₁ = 0.35 and x₂ = 0.60 were observed and studied. These phenomena were found to be related to the dynamics of charge localization on defects with activation energies of U_a1 ≈ 0.6 eV and U_a2 ≈ 0.23 eV. Relaxator behavior appears when the Curie point lies in the temperature region of thermal charge localization. The concentration dependence features at x₁ and x₂ are explained by the coincidence of the Curie point and the centers of the temperature regions of charge localization on the U_a1 and U_a2 defect levels, respectively.     

Relaxation Processes and Coherent Spin Manipulations for Triplet Si–C Divacancies in Silicon Carbide Enriched Tenfold in the 13C Isotope

JETP Letters - Coherent spin manipulations of ensembles of color centers in the form of neutral VSi–VC divacancies with the spin $$S = 1$$ in hexagonal silicon carbide 6H–SiC enriched...     

Nitrogen-containing species in the structure of the synthesized nano-hydroxyapatite

Synthesized by the wet chemical precipitation technique, hydroxyapatite (HAp) powders with the sizes of the crystallites of 20–50 nm and 1 μm were analyzed by different analytical methods. By means of electron paramagnetic resonance (EPR) it is shown that during the synthesis process nitrate anions from the reagents (byproducts) could incorporate into the HAp structure. The relaxation times and EPR parameters of the stable axially symmetric NO ₃ ^2? paramagnetic centers detected after X-ray irradiation are measured with high accuracy. Analyses of high-frequency (95 GHz) electron-nuclear double resonance spectra from ¹H and ³¹P nuclei and ab initio density functional theory calculations allow suggesting that the paramagnetic centers and nitrate anions as the precursors of NO ₃ ^2? radicals preferably occupy PO ₄ ^3? site in the HAp structure.     

Coherence times and Rabi oscillations in CaWO₄:Cr(5+) crystal

The coherence times of dopant pentavalent chromium ions in CaWO? single crystal (0.0006at.% Cr(5+)) were investigated both theoretically and experimentally. Temperature dependences of spin-lattice relaxation time T? and phase memory time T(M) were measured in the temperature range 6-30 K at high (94 GHz, W band) and low (3.5 GHz, S band) frequencies of electron spin resonance. It follows from T(M) calculations that phase relaxation of Cr(5+) ion arises mainly from magnetic dipole interactions between the chromium ions. Anomalously fast damping of Rabi oscillations is detected in both S- and W-band experiments. It is shown that this phenomenon is caused by microwave field inhomogeneity inside the resonator. Relations between the damping time of Rabi oscillations, Rabi frequency and the crystal sample size are obtained. Lumped-element resonators and smaller sample dimensions are suggested to lower spin dephasing during transient nutations.     

Quantum chemical study of the addition of ozone to acetylene

The primary step of acetylene ozonation was studied by the B1LYP, PBE0, CASSCF, MRMP2, and CCSD methods using the 6-31+G**, aug-cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ basis sets. The study confirmed the earlier B3LYP-based conclusions that the intermediate complex, as well as the transition states of the concerted addition (Criegee’s mechanism) and unconcerted addition (DeMore’s mechanism), are involved in this reaction event. The activation enthalpy and entropy and rate constants of the reaction were calculated. Criegee’s mechanism was shown to dominate in the reaction with acetylene, but the contribution from DeMore’s mechanism is also noticeable, being 1–8%.     

Electronic Properties of a Two-Dimensional Electron Gas at the Interface between Transition Metal Complex Oxides

The structural and electronic properties of heterostructures based on transition metal oxides containing strongly correlated electrons are compared. The investigated structures are LaAlO₃/SrTiO₃ (LAO/STO), LaAlO₃/BaTiO₃ (LAO/BTO), and BaTiO₃/SrTiO₃ (BTO/STO). The role of structural relaxation in the formation of a two-dimensional electron gas at the interface of two dielectrics is revealed. The contribution from different orbitals and atoms to conductivity is analyzed, along with the correlation between structural distortions induced by the dipole moment in an LAO layer and conductivity.     

Quantum-Chemical Study of Stressed Polyethylene and Butadiene Rubber Chain Scission

The thermal decomposition of polyethylene and butadiene rubber chains in the presence of a tensile force acting along the axis of the molecule was simulated. The reaction of an isolated chain was considered. The chain models were the octane and 2,6-octadiene molecules. A deformation was introduced in the problem by fixing nonequilibrium distances between the terminal carbon atoms. The reaction coordinate (the middle C–C bond length R) was scanned at a fixed length of the molecule (L). That is, the potential energy surface section of the reaction was constructed at L = const. The reaction sensitivity to deformation was evaluated by B3LYP, LC-ωPBE, CCSD(T), CASSCF, and MP2 quantum-chemical calculations. All these calculations showed that the molecule elongated by ~1 Å for polyethylene, but shortened by 0.3–0.5 Å for 2,6-octadiene during chain scission. This means that the tensile deformation accelerates the decomposition of polyethylene, but decelerates the decomposition of butadiene rubber.     

Stationary and high-frequency pulsed electron paramagnetic resonance of a calcified atherosclerotic plaque

New possibilities of applying high-frequency electron paramagnetic resonance in medicine are demonstrated on an example of the investigation of a calcified atherosclerotic plaque. After the irradiation of the atherosclerotic plaque by x rays, a new type of paramagnetic centers—organomineral radicals—is detected. The spectral and relaxation characteristics of these radicals depend on the calcification degree of the atherosclerotic plaque and can be used for diagnostics.