From crystal to glass-like thermal conductivity in crystalline minerals

Abstract

The ability of some materials with a perfectly ordered crystal structure to mimic the heat conduction of amorphous solids is a remarkable physical property that finds applications in numerous areas of materials science, for example, in the search for more efficient thermoelectric materials that enable to directly convert heat into electricity. Here, we unveil the mechanism in which glass-like thermal conductivity emerges in tetrahedrites, a family of natural minerals extensively studied in geology and, more recently, in thermoelectricity. By investigating the lattice dynamics of two tetrahedrites of very close compositions (Cu12Sb2Te2S13 and Cu10Te4S13) but with opposite glasslike and crystal thermal transport by means of powder and single-crystal inelastic neutron scattering, we demonstrate that the former originates from the peculiar chemical environment of the copper atoms giving rise to a strongly anharmonic excess of vibrational states.

First-principles studies of atomic dynamics in tetrahedrite thermoelectrics

“…8 As discussed previously, experimental INS data showed that the low energy modes (∼4 meV) shifted to lower energies with the decrease of temperatures, i.e., phonon softening upon cooling, for both Cu 10 Zn 2 Sb 4 S 13 and Cu 10 Zn 2 Sb 2 Te 2 S 13 tetrahedrites. 9 A similar feature was also observed in Cu 10.5 NiZn 0.5 Sb 4 S 13 (data not shown). To understand the nature of this softening, we investigated the temperature dependence of the low energy modes in Cu 10.5 NiZn 0.5 Sb 4 S 13 by looking into the FPMD trajectories.…”

“…8 Another type of anomalous behavior is the phonon softening upon cooling, or stiffening upon heating, revealed by inelastic neutron scattering (INS) experiments, in which the decrease of low-energy vibration mode energies with the decrease of temperatures was observed. 9 While it was argued that this anomaly is also related to the dynamics of Cu12e, the detailed atomic mechanism remains elusive.…”

“…The energies of the low-energy peak remain constant at ∼3.25 meV between 50 K and 100 K and shifted to higher values as the temperature is increased, i.e., ∼3.5 meV at 200 K and ∼4 meV at 300 K. This observation of "phonon softening upon cooling" is consistent with what was found from experimental INS data. 9 To gain atomic insight into the mechanism of this anomaly, we examined the relative distance of Cu12e atom to the two Sb atoms inside the Sb[CuS 3 ]Sb cage, shown schematically in Figure 3(e). The lone pair electrons (crescent) of Sb modulate the motion of the Cu12e atom and are responsible for its anharmonic rattling, according to our previous work.…”

Research Update: Cu–S based synthetic minerals as efficient thermoelectric materials at medium temperatures

“…38 In Cu 12 Sb 2 Te 2 S 13 , the characteristic energy for the out-of-plane vibration mode of Cu(2) increased from 2.5 to 4.0 meV on heating from 2 K to 200 K, indicating the strong anharmonicity of the mode. 67 The low-energy weakly dispersive optical branch being coupled with acoustic phonons has been considered as the cause of low κ L of the tetrahedrite.…”

Tetrahedrites: Prospective Novel Thermoelectric Materials

“…The large and anisotropic thermal displacement parameters of the Cu2 atoms had been thought to play a major role in disrupting eiciently the heat-carrying acoustic waves. A detailed study of the latice dynamics of tetrahedrites has been undertaken recently using a combination of inelastic neutron scatering on poly-and single-crystalline tetrahedrites [46]. The conventional temperature dependence of the latice thermal conductivity in the Cu-deicient tetrahedrite Cu 10 Te 4 S 13 ofered an interesting experimental platform to unveil the microscopic mechanisms responsible for the low, glass-like thermal conductivity of tetrahedrites (Figure 7).…”