Climatic variability of the mean flow and stationary planetary waves in the NCEP/NCAR reanalysis data

NCEP/NCAR (National Center for Environmental Prediction – National Center for Atmospheric Research) data have been used to estimate the long-term variability of the mean flow, temperature, and Stationary Planetary Waves (SPW) in the troposphere and lower stratosphere. The results obtained show noticeable climatic variabilities in the intensity and position of the tropospheric jets that are caused by temperature changes in the lower atmosphere. As a result, we can expect that this variability of the mean flow will cause the changes in the SPW propagation conditions. The simulation of the SPW with zonal wave number <I>m</I>=1 (SPW1), performed with a linearized model using the mean flow distributions typical for the 1960s and for the beginning of 21st century, supports this assumption and shows that during the last 40 years the amplitude of the SPW1 in the stratosphere and mesosphere increased substantially. The analysis of the SPW amplitudes extracted from the geopotential height and zonal wind NCEP/NCAR data supports the results of simulation and shows that during the last years there exists an increase in the SPW1 activity in the lower stratosphere. These changes in the amplitudes are accompanied by increased interannual variability of the SPW1, as well. Analysis of the SPW2 activity shows that changes in its amplitude have a different sign in the northern winter hemisphere and at low latitudes in the southern summer hemisphere. The value of the SPW2 variability differs latitudinally and can be explained by nonlinear interference of the primary wave propagation from below and from secondary SPW2

Structural, thermal and optical properties of elpasolite-like (NH4)2KZrF7

New fluoride compound (NH4)2KZrF7 with the elpasolite structure (sp. gr. Fm-3m) was synthesized by partial cationic substitution in (NH4)3ZrF7 cryolite. Due to small difference in ionic radii of K+ and NH+ , non-equivalent crystallographic positions 8c and 4b are occupied by both cations. Investigations of thermal, optical and structural properties in a wide range of temperature revealed two phase transitions Fm-3m ↔ P42/ncm ↔ P42/nmc of the first order. The results obtained are discussed in comparison with the data for the previously studied related cryolite (NH4)3ZrF

Effect of Deuteration on Phase Transitions in Vanadium Dioxotetrafluoride

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.The crystals of (ND4)3VO2F4 with a high degree of deuteration (~87%) have been grown and a significant (~1.5%) increase in the unit cell volume has been detected. The decrease in the chemical pressure leads to a change in the sequence of phase transitions due to wedging-out of one of the rhombic phases observed in (NH4)3VO2F4. The thermal physical studies have been carried out and the entropies, deformations, and pressure coefficients related to structural transformations have been determined. The T–p phase diagram has been built and the pressure and temperature boundaries of crystal phase stability have been determined. The dielectric studies demonstrate a nonferroelectric nature of the phase transitions in (ND4)3VO2F4. The experimental and model entropies are compared. Based on the decrease in the entropy as a result of deuteration, a hypothesis on significant but not limited anharmonism of vibrations of ammonia tetrahedral corresponding to the disordering is proposed

Mixed-valence hydrated iron fluoridotitanate: Synthesis, optics and calorimetry

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Mixed-valence hydrated fluoridotitanate with idealized formula FeTiF6·6H2O is the main product of fluoride processing of natural mineral ilmenite with hydrofluoric acid. Its single crystals were grown and optical and calorimetric experiments were carried out in the temperature range 200–350 K. Charge re-distribution, Fe2+Ti4+ to Fe3+Ti3+, in the compound studied was evident in XPS spectra. A first order ferroelastic phase transition occurs at temperatures T0↓ = 271.5 K, T0↑ = 274 ÷ 275.5 K with the symmetry change P3‾↔ P1‾. The structural transformation is accompanied by the appearance of a very weak optical anisotropy in the slice (001), a small anomaly of the heat capacity (ΔS = 1.5 J/mol K = 0.2R), and positive baric coefficients dT0/dp ≈ 30 ± 10 K/GPa. © 2020 Elsevier Lt

Sequence of phase transitions in (NH4)3SiF7

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Single crystals of silicon double salt (NH4)(3)SiF7 = (NH4)(2)SiF6 center dot NH4F = (NH4)(3)[SiF6]F were grown and studied by the methods of polarization optics, X-ray diffraction and calorimetry. A sequence of symmetry transformations with the temperature change was established: P4/mbm (Z = 2) (G(1)) Pbam (Z = 4) (G(2)) P2(1)/c (Z = 4) (G(3)) P (1) over bar (Z = 4) (G(4)) P2(1)/c (Z = 8) (G(5)). Crystal structures of different phases were determined. The experimental data were also interpreted by a group-theoretical analysis of the complete condensate of order parameters taking into account critical and noncritical atomic displacements. Strengthening of the N-H center dot center dot center dot F hydrogen bonds can be a driving force of the observed phase transitions

Sequence of phase transitions in (NH4)3SiF7

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Single crystals of silicon double salt (NH4)(3)SiF7 = (NH4)(2)SiF6 center dot NH4F = (NH4)(3)[SiF6]F were grown and studied by the methods of polarization optics, X-ray diffraction and calorimetry. A sequence of symmetry transformations with the temperature change was established: P4/mbm (Z = 2) (G(1)) Pbam (Z = 4) (G(2)) P2(1)/c (Z = 4) (G(3)) P (1) over bar (Z = 4) (G(4)) P2(1)/c (Z = 8) (G(5)). Crystal structures of different phases were determined. The experimental data were also interpreted by a group-theoretical analysis of the complete condensate of order parameters taking into account critical and noncritical atomic displacements. Strengthening of the N-H center dot center dot center dot F hydrogen bonds can be a driving force of the observed phase transitions

Influence of thermal conditions on the electrocaloric effect in a multilayer capacitor based on doped BaTiO3

We present the results of studies of thermal expansion, heat capacity, permittivity, polarization and the influence of different thermal conditions on the intensive electrocaloric effect (ECE), ΔTAD, in a commercial multilayer capacitor based on doped BaTiO3. Investigations in a wide temperature range revealed one anomaly in the behavior of the physical properties at about 290K characteristic for the relaxors. Direct measurements showed a high reversibility of ECE under equilibrium thermal conditions. Good agreement was found between the values of ΔTAD determined by direct and indirect measurements at the electric field up to 15.4kV/cm. Quasi-isothermal conditions lead, firstly, to decrease of large ΔTAD≈0.94K obtained in adiabatic conditions under E=308kV/cm to 0.87K, and, secondly, the appearance of a difference between the values of ΔTON and ΔTOFF determined when the electric field is applied and removed. Using this phenomenon and changing the frequency of the periodic electric field, E=15.4kV/cm, the effect of cooling was obtained equal to [(ΔTON+ΔTOFF)∕2]max=−0.032K. The results obtained are useful for further development of the electrocaloric refrigeration technique without thermal switches