engleski

Thermal conductivity of (Ta1-xNbxSe4)2I alloys

We present measurements and analysis of the phonon thermal conductivity k(T) of the alloys of the linear-chain compounds (TaSe4)2I and (Ta0.99Nb0.01Se4)2I, in the temperature range 60mK-6K. k(T) shows a very sharp peak in the vicinity of 1K and 2K for a (TaSe4)2I and (Ta0.99Nb0.01Se4)2I, respectively. The appearance of the peak in these systems is explained by a Poiseuille flow of phonons, originating from their strong anharmonicity amplified by the lattice anisotropy. k(T) of (TaSe4)2I obeys cubic variation (kľT3) below 0.8K, in good agreement with the boundary scattering regime. While k(T) of (Ta0.99Nb0.01Se4)2I and (TaSe4)2I (remeasured after a long storage at room temperature, and several thermal cycles down to 4K) in the temperature range 0.1K-1K and 60mK-6K, respectively, obeys quasi-quadratic regime (kľT1.8). This is ascribed to extended "linear or planar defects" specific to this very anisotropic structure, introduced either by doping Nb atoms in (TaSe4)2I or by successive thermal cycling. Below 0.1K, k(T) of (Ta0.99Nb0.01Se4)2I follows a cubic variation in good agreement with the boundary scattering regime.

lattice thermal conductivtiy; lattice anharmonicity; quasi-one dimensional semiconductors

Predavač dr. sc. Ana Smontara.