Dielectric properties of crystalline binary KNO3—AgNO3 mixtures embedded in nanoporous silicate matrices

The results of dielectric studies of MCM-41 sili cate matrices with cellular pores (37.0 and 26.1 ? in diameter) filled by binary mixtures of K_1−x Ag _x NO₃ (x=0, 0.05, 0.10) are reported in comparison with those obtained for bulk salts of the same composition in the temperature range of structural phase transitions. It has been revealed that, upon heating, the nanocomposites undergo transitions from crystal modification II to phase I, as in bulk KNO₃, whereas the bulk mixtures with x=0.05 and 0.10 have a complex structure in accordance with the phase diagram. It has been shown that embedding binary salts and pure potassium nitrate in pores with a diameter of 26.1? results in the formation of an intermediate ferroelectric phase upon cooling. The permittivity and electrical conductivity are found to increase with increasing AgNO₃ concentration in bulk samples, as well as with decreasing pore size in the nanocomposites for all values of x.     

Temperature features of ultrasonic attenuation in photochromic glasses with copper chloride nanocrystals

The results of acoustooptic measurements of the attenuation coefficient of longitudinal ultrasonic waves in copper halide photochromic glasses are presented for wide temperature (140–550 K) and frequency (190–790 MHz) ranges. In the low-temperature region (T < 230 K), a wide relaxational peak is observed at a frequency of 629 MHz. Presumably, this peak is related to the motion of copper ions in the glass lattice. In the high-temperature region (up to 550 K), the attenuation coefficient does not depend on temperature. The presence of the temperature plateau is explained in the framework of the two-level system model with weak asymmetry.     

MAS NMR studies of nanoporous matrices filled with sodium nitrite

The sodium nitrite NaNO2 incorporated into MCM-41 molecular sieves with pore sizes of 20, 26, and 37 Å has been investigated by 23Na magic-angle spinning NMR spectroscopy. It has been demonstrated that the structure of the crystalline phase of the nitrite in a confined geometry is similar to the structure of bulk nitrite NaNO2. The direct proof of the diffuse melting of sodium nitrite in the pores has been obtained. The NMR signal of the molten sodium nitrite phase has been observed at temperatures close to the completion of the melting.     

<Superscript>77</Superscript>Se Low-Temperature NMR in the Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> Single Crystalline Topological Insulator

⁷⁷Se nuclear magnetic resonance (NMR) measurements in the Bi₂Se₃ topological insulator single crystal were carried out at temperatures 15.8, 88, and 293 K. Bismuth selenide single crystalline plate was studied in the orientation when the crystallographic c-axis was parallel to the external magnetic field B₀. We observed two component NMR spectra at the three temperatures. It was shown that the NMR spectrum almost did not move with decreasing temperature and the density of charge carriers did not follow the thermal activation law.     

Influence of the geometry of a porous network on the phase transition in a ferroelectric embedded in a porous matrix

A ferroelectric phase transition in a system of electrically interacting small particles is considered. The size effects in a single particle are described in terms of the Landau phenomenological model. The interaction between particles is reduced to a dipole-dipole interaction. It is shown that the interparticle interaction can lead to a substantial increase in the phase transition temperature as compared to the temperature of the ferroelectric transition in a single small particle.     

Spin-lattice relaxation enhancement in liquid gallium confined within nanoporous matrices

Nuclear spin relaxation for liquid gallium embedded into nanoporous matrices was found to accelerate remarkably compared to the bulk melt. NMR measurements on two gallium isotopes showed that the dominant mechanism of relaxation was changed from magnetic to quadrupolar and the relation rate depended on the Larmor frequency. The correlation time of electric field gradient fluctuations was estimated using data for quadrupolar relaxation contribution and was found to increase drastically compared to bulk, which corresponded to slowing down mobility in confined liquid gallium.     

The growth of a single crystal of Sr3CuIrO6 and its magnetic behavior compared to polycrystals

We have grown single crystals of the psuedo-one-dimensional compound Sr₃CuIrO₆, a K₄CdCl₆-derived monoclinic structure with Cu-Ir chains along the [101] direction. We present the ac and dc magnetization behavior of the single crystals in comparison with that of the polycrystalline form reported earlier. There is a distinct evidence for at least two magnetic transitions, at 5 K (T ₁) and 19 K (T ₂), with different relative magnitudes in the single and polycrystals. The low temperature magnetic relaxation behavior of both the forms is found to be widely different, exhibiting unexpected time dependence.     

Effect of substitutional order on the relaxation of aluminum nuclei in Y<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Lu<Subscript>x</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> mixed garnets

The spin-lattice relaxation time of ²⁷Al nuclei residing in the octahedral and tetrahedral oxygen environment in Y_{3 ?x}Lu_xAl₅O₁₂ mixed aluminum-yttrium garnets was measured by the NMR method for 0≤x≤3. A maximum in the concentration dependence of the relaxation time was observed for both crystallographic positions at x=0.75; this maximum correlates with the minimum in the NMR linewidth, indicating the ordering obtained as the yttrium and lutetium ions occupy the dodecahedral positions in the garnet lattice.     

Acoustic study of the melting and solidification of gallium incorporated in an opal matrix

An acoustic study is reported of the crystallization and melting of gallium embedded in an opal-like matrix. The variations of the velocity and absorption of longitudinal ultrasonic waves during phase transitions in the α and β modifications have been found to be hysteretic in nature. It is shown that acoustic methods do not detect gallium melting and crystallization in the tetragonal phase forming in a restricted geometry. Experimental evidence for heterogeneous crystallization of gallium in pores has been obtained.