TlFeX2 (X = S, Se) compounds crystallike as a chain structure in the form of long brittle filaments /1, 2 1 . Their monoclinic structure includes infinite chains (FeX2) built from FeX4 tetrahedra with mutual edges. Exchange interactions between the iron ions along the chain are realized by the chain of Fe-X-Fe configurations while within the FeX4 tetrahedron perpendicular to the chain directions they are realized by FE-X-T1-X-Fe configurations. Therefore one can assume that the strong difference between exchange interaction energies inside and between the chains leads to pseudo-one-dimensional magnetic structures of TlFeS2 and TlFeSe2.The aim of the present note is to investigate the influence of space-like and spin dimensions of the TlFeS2 and TlFeSe2 magnetic semiconductors on the behavior of heat capacity and magnetic susceptibility. The heat capacity (C ) is measured by the adiabatic method, and the magnetic susceptibility (x) by the Faraday method within the temperature range 4.2 to 300 K . The TlFeS2 and TlFeSe2 specimens were synthesized by reaction of the initial components in quartz ampoules / I / . Fig. l a and b show the results of heat capacity measurements of TlFeS2 and T1FeSe2. As is seen from the figures, a X anomaly characteristic of magnetic transitions is not detected in the C (T) dependence. W e could not find the corresponding isomorphic diamagnetic component in order to separate the lattice (Cht) and magnetic ( C ) contributions of the heat capacity for T1FeS2. As it is known, for this purpose Tarasov's model / 3 / o r its modified form / 4 , 51 is also used in the region Clat >> C which is suitable for describing the lattice heat capacity of layered and chain compounds using a smaller number of adjustable parameters. The analysis showed that the heat capacity of T1FeS2 from ;a200 to 80 K is well described by Tarasov's model for chain structures with el = 455 K and O3 = 91 K. At a200 K Cexp is about 2 % greater than Ctheor which is closer to the difference between C and Cv in this temperature range. Fig. l a also
In recent years growing interest has been expressed in obtaining information on the lattice dynamics of solids on the basis of experimental data on the heat capacity at low temperatures. This is accounted for by the fact that a comparison between experimental and theoretical results of phonon spectrum investigations allows one to choose or refine the parameters of a given theoretical model.The present report deals with an investigation of the heat capacity of TlGaTe2 in the temperature range from 5 to 300 K. Some phonon spectrum characteristics have been calculated, namely the n-th moments , w = (1/3N) J"." G(v)dv , 0 ; the Debye temperature at T-oo, @g),the temperature related to the entropy at T+-, v the geometric mean frequency, and EZ the zero vibrational energy of TlGaTe2 atoms in a harmonic approximation,The TlGaTe2 compound crystallizes in a TlSe-type complex chain structure /l/, TlGaTe2 specimens were obtained by fusing the initial components in evacuated and sealed quartz ampoules. A vacuum adiabatic unit with an automatic temperature control was used to measure C (T) /2/. The heat-capacity measurement e r r o r s amounted to 3 to 5% below 10 K, and 0.2 to 0.3% in the range from 10 to 300 K.The results of experimental heat-capacity measurements are depicted in Fig. 1. Inasmuch as the heat capacity of TlGaTe2 was measured for the first time, it was studied over the entire temperature range without any omissions. The heat-capacity behaviour failed to exhibit any anomalies due to phase transitions. 0 9 P Fig. 1 also gives the temperature dependence oi the Debye temperature QD calculated on the basis of levelled-off heat-capacity values. Below s s 8 K the 1) prospekt Narimanova 33, 370143 Baku, USSR.
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