The crystal and magnetic structures of TlFeS 2 and TlFeSe 2 chalcogenides are studied by neutron diffraction in the temperature range 10-300 K. The investigated compounds feature monoclinic crystal sym metry with the C2/m space group. Antiferromagnetic ordering occurs in TlFeS 2 and TlFeSe 2 at the Néel tem perature T N = 210(5) and 295(5) K, respectively. The temperature dependences of magnetic moments, Fe-Fe bond lengths, and unit cell volume are established. The coefficients of thermal expansion for the paramag netic and antiferromagnetic phases are calculated.

The crystal structure of the semiconductors TlFeSe 2 and TlFeS 2 has been studied by mean of neutron diffraction at room temperature and high pressure up to 4.2 GPa and 5.2 GPa, respectively. The chain-like monoclinic crystal structure with space group C2/m remains unchanged in both compounds in the entire pressure range. The anisotropic lattice compression and the large difference in the bulk modulus and the compressibility coefficients of the structural parameters of the two compounds have been observed. The mechanism of the observed phenomena was discussed. The enhancement of the onedimensional antiferromagnetic and metallic character was predicted.

The crystal and magnetic structures of TlFeS 2 and TlFeSe 2 are studied by neutron diffraction in the temperature range of 10-320 K. The structures of TlFeS 2 and TlFeSe 2 have monoclinic symmetry with the space group C2/m at room temperature. TlFeS 2 displays an antiferromagnetic phase at temperature below 200 K. The antiferromagnetic phase transition in TlFeSe 2 takes place at a temperature below 290 K. The tem perature dependence of the unit cell parameters and volume are obtained. The coefficients of thermal and linear expansion are calculated. The temperature dependences of the interatomic distances are presented.

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