Thermoelectric properties of CeNi2Al3 compound: an experimental and theoretical study

We present thermoelectric properties of the CeNi2Al3 compound in the temperature range from 4 to 300 K. The electrical resistance (ρ) exhibits a metallic-like character reaching approximately 50 μΩ cm at room temperature. The temperature dependence of the Seebeck coefficient (S) is typical for mixed valence compounds having positive values with a broad maximum (~ 46 μV/K) over a wide temperature range from 200 to 300 K. The thermal conductivity (κ) value reaches 15 W/(m K) at T = 300 K. The power factor (PF = S2/ρ) at 150 K is high (~ 70 μW/cm K2), larger than for conventional thermoelectric materials based on Bi2Te3. The dimensionless figure of merit (ZT) has a broad maximum over a wide temperature range, which reaches the value of 0.1 around 220 K. The experimental results are supported by calculations within the density functional theory (DFT) performed on the basis of the full-potential local-orbital minimum-basis scheme (FPLO). The coherent potential approximation (CPA) is used to simulate the chemical disorder. The calculations are focused on the site preference of Ni and Al atoms. Investigations of the energetic stability have shown that in CeNi2Al3 the aluminum atoms prefer the 3g sites and the nickel ones the 2c sites.

The daylight climate of Athens: Variations and tendencies in the period 1992–2017, the brightening era

Though numerous daylight studies have been conducted worldwide, works for the daylight climate and/or the daylight variations/trends are rare. This gap is treated here. Therefore, the innovative trend analysis and the month–hour diagrams are applied to the illuminance time series at Athens over the period of 1992–2017 under all-/clear-sky conditions. For all skies, the global illuminance shows a broad maximum at summer noon, while the diffuse counterpart is in spring. Under clear skies, the global illuminance maximum becomes broader, covering spring/summer. However, the diffuse illuminance maximum splits into minor ones in April and June. The innovative trend analysis method finds that the identified trends are + 2.83%/decade (−1.89%/decade) for the global (diffuse) illuminance, under all skies. In clear skies, the above values are modified to +2.66%/decade (−2.00%/decade). These results confirm a recovery in the Athens daylight levels as in the solar radiation ones found by many researchers. Another outcome of the study concerns the observed decline in diffuse illuminance levels in the examined period, which may be attributed to a decline in cloudiness and an increase of sunshine over the area. Also, the variation of the global and diffuse illuminance efficacies on a month–hour basis is examined using the month–hour diagram method.

Synthesis and Electroluminescent Property of Bis{2-(naphtha [3,4]imidazol-2-Yl) Pyridinato} Magnesium

An emission material, bis{2-(naphtha [3,4]imidazol-2-yl) pyridinato} Magnesium (MgNIP) used for organic light emitting devices, has been synthesized. The decomposition temperature was observed at 510°C and no melting transition (Tm) of MgNIP was observed up to 400°C. The emission spectrum of organic emitting device using MgNIP as emitted layer exhibits a broad maximum at 531 nm. The color of the emitted light is in the orange region in the CIE coordinate of x = 0.46 y = 0.46.

MECHANISM OF MgB2 SUPERCONDUCTIVITY WITH INTERBAND PAIR-TRANSFER INTERACTION

A two-band scheme of MgB2 superconductivity is developed. It comprises repulsive interband transfer of intraband pairs between effective σ- and π-bands together with σ-intraband electron–phonon attraction and Coulomb interaction. The interaction constants are found by fitting T c , specific heat jump and zero-temperature gaps ratio. The gaps and specific heat dependences on temperature besides the T c isotope effect exponent, calculated without any additional free parameters, agree with the experiment. T c versus chemical potential shows a broad maximum to which the "autodoped" MgB2 belongs.

Dielectric properties of BaTiO3–BaZrO3 ceramics under a high electric field

Multilayered ceramic capacitors (MLCCs) with BaTiO3–BaZrO3 (BTZ) dielectric layers were fabricated, and the dielectric permittivity of the BTZ layers with different thicknesses in MLCCs was measured. The dielectric permittivity of the BTZ ceramic disk was also measured under various ac electric fields. The variation in the dielectric behaviors with the thickness of BTZ layers in MLCCs was explained by the ac-field dependence of dielectric permittivity observed in the BTZ ceramic disk. The ac-field dependence of dielectric permittivity of BTZ was markedly observed below the temperature of a broad maximum in the dielectric permittivity versus temperature (є versus T) curve. It was found that the temperature of the broad maximum shifted to the low-temperature side and the peak shape became asymmetric with increasing ac field. These changes in the dielectric properties under high ac fields were explained by a model of relaxors with the concept of the formation of polar microregions (PMRs) and the freezing of fluctuating ipoles in PMRs.

Thermoelectric Power of YBa2Cu3O7-Xand YBa2Cu4O8Under Pressure

Thermoelectric power (TEP) of YBa2Cu3O7-X(123) and YBa2Cu4O8(124) samples are measured as a function of pressure. The TEP of an as-sintered 123 polycrystalline sample shows a broad maximum around 1.25 GPa whereas that of the cold-pressed sample decreases steadily. The ab-plane TEP of 123 single crystal decreases monotonically and the c-axis TEP exhibits a maximum around 1.5 GPa. Disappearance of the broad maximum in the polycrystalline sample upon cold-pressing is interpreted in terms of the crystallite orientation occurring under pressure. TEP of the 124 polycrystalline sample decreases sharply up to 4.5 GPa and at a lower rate with further increase in pressure, a trend similar to that is observed in the variation of Tcas a function of pressure.

MARTENSITIC TRANSFORMATION AND MAGNETIC PROPERTIES OF Fe-Pd ALLOYS

The effects of martensitic transformation from fcc to fct structure on the magetic properties of Fe-Pd alloys are investigated by magnetization, magnetostriction and 57Fe Mössbauer effect measurements. In the composition range of 30–32.5 at .% Pd, in which the fcc-fct transformation occurs, the Curie temperature decreases sharply with decreasing Pd content and the magnetostriction vs. temperature curve has a broad maximum around the fcc-fct transformation temperature. The Mössbauer spectrum exhibits the difference between the internal field for fcc, and fct.

Infrared Absorption and Reflection Spectra of Crystalline TCNQ Salts

The polarised absorption and reflectance spectra of the three TCNQ salts pyridinium (TCNQh, triethylammonium (TCNQh and thermally damaged quinolinium (TCNQh indicate that the absorption features are governed by reflection characteristics. The maximum reflectance curve shows a broad minimum which corresponds to a negative dip in the real part of the dielectric constant and a broad maximum in the imaginary part, as calculated using a Kramers-Kronig

ULTRASONIC ATTENUATION MEASUREMENTS ON LuBa2Cu3O7 AND HoBa2Cu3O7

HoBa 2 Cu 3 O 7 and LuBa 2 Cu 3 O 7 show very different ultrasonic attenuation behavior at temperatures below 220 K. The Ho sample exhibits a broad maximum in attenuation at around 220 K, while the Lu sample shows a minimum followed by a plateau below 140 K. At T c , the Ho sample shows a decrease in attenuation; there is no evidence for such a change in the Lu sample.