Lyudmila N. Reshetova

Impedance of Sn24P19.3BrxI8−x semiconducting clathrates

The temperature and frequency dependences of the real and imaginary parts of the complex impedance of ceramic samples of the clathrates of variable composition Sn24P19.3BrxI8−x are investigated in the frequency range from 20 to 106Hz at temperatures from 4.2 to 200K. The conductivity of the samples is measured in the dc regime at temperatures from 4.2 to 300K; it is characterized by the presence of an activation part, with energy increasing monotonically from 18 to 77meV as the bromine concentration increases. The impedance spectra are investigated by a graphoanalytical method. As an approximating equivalent circuit, an RC circuit with a frequency-dependent capacitance is considered. It is shown that the capacitive contribution to the admittance falls off sharply with decreasing temperature below 75K and with increasing frequency above 150kHz. The observed dielectric anomalies are attributed to a substantial contribution to the complex impedance from the grain boundaries.

On the crystal structure of the germanium-based cationic clathrates [Ge38.3Sb7.7]I7.44, [Ge38.1P7.9]I8, and [Ge30.5Sn7.7P7.75]I7.88

Compounds [Ge38.3Sb7.7]I7.44, [Ge38.1P7.9]I8, and [Ge30.5Sn7.7P7.75]I7.88 with the clathrate type-I structure were synthesized. They crystallize in the cubic space group

Novel compounds Sn20Zn4P22-νI8 (ν = 1.2), Sn17Zn7P22I8, and Sn17Zn7P22Br8: Synthesis, properties, and special features of their clathrate-like crystal structures

Pm\bar 3n

The behaviour of beryllium μ4-oxo-μ-carboxylates under electron impact

with the unit cell parameter a = 10.8592(9), 10.4983(12), and 10.7210(10) Å (Z = 1), respectively. Their crystal structure represents the germanium(tin)-pnictogen framework, capturing the guest iodine anions in its cavities. All compounds have no vacancies in the host substructure; however, two of them show vacancies in the guest positions. The atomic distribution over the framework sites is of the most interest as it follows trends associated with the relative electronegativities of the atoms composing the framework. The results of the band structure calculations and application of the Zintl counting scheme are also discussed in relation to potential thermoelectric properties.

Mass spectrometric study of μ4-oxohexa-μ-acetatotetrazinc, Zn4O(CH3CO2)6

Inorganic clathrate materials are of great fundamental interest and potential practical use for application as thermoelectric materials in freon-free refrigerators, waste-heat converters, direct solar thermal energy converters, and many others. Experimental studies of their electronic structure and bonding have been, however, strongly restricted by (i) the crystal size and (ii) essential difficulties linked with the clean surface preparation. Overcoming these handicaps, we present for the first time a comprehensive picture of the electronic band structure and the chemical bonding for the Sn(24-x-δ)InxAs(22-y)I8 clathrates obtained by means of photoelectron spectroscopy and complementary quantum modeling.