Thermal Conductivity of HfTe₅: A Critical Revisit

Abstract

Hafnium pentatelluride (HfTe 5 ) has attracted extensive interest due to its exotic electronic, optical, and thermal properties. As a highly anisotropic crystal (layered structure with in-plane chains), it has highly anisotropic electrical-transport properties, but the anisotropy of its thermal-transport properties has not been established. Here, accurate experimental measurements and theoretical calculations are combined to resolve this issue. Time-domain thermoreflectance measurements find a highly anisotropic thermal conductivity, 28:1:8, with values of 11.3 ± 2.2, 0.41 ± 0.04, and 3.2 ± 2.0 W m -1 K -1 along the in-plane a-axis, through-plane b-axis, and in-plane c-axis, respectively. This anisotropy is even larger than what was recently established for ZrTe 5 (12:1:6), but the individual values are somewhat higher, even though Zr has a smaller atomic mass than Hf. Density-functional-theory calculations predict thermal conductivities in good agreement with the experimental data, provide comprehensive insights into the results, and reveal the origin of the apparent anomaly of the relative thermal conductivities of the two pentatellurides. These results establish that HfTe 5 and ZrTe 5 , and by implication their alloys, have highly anisotropic and ultralow through-plane thermal conductivities, which can provide guidance for the design of materials for new directionalheat-management applications and potentially other thermal functionalities.

Phonon anharmonicity of thermoelectric material HfTe5 studied by Raman spectroscopy

“…This lattice anisotropy may also induce intriguing phenomena such as crystallographic orientation-dependent thermal conductivity in HfTe 5. [12] Figure 2c reveals quasi-2D layers indeed pile up along b axis, forming desired layer structure. The layered structure provides the ability to mechanically exfoliate HfTe 5 crystals for extra low dimensional studies.…”

“…The reduction of thermal conductivity will improve heat-to-electricity energy conversion efficiency, enabling great advancement in thermoelectrics performance. Although ZrTe 5 and HfTe 5 behave like semimetals, an ultralow through-plane thermal conductivity as small as 0.33 ± 0.03 W m −1 K −1 [11] and 0.41 ± 0.04 W m −1 K −1 [12] at room temperature have been demonstrated recently, even lower than 1.0 W m −1 K −1 that of commercial thermoelectric materials. [9,10] The low thermal conductivity motivated further exhaustive researches on the underpinning mechanism.…”

“…[4][5][6][7] Beyond topological characteristics, pentatellurides also have attracted more and more attention because of their efficient thermal properties. [8][9][10][11][12] Generally, the efficiency of thermoelectric materials is determined by the dimensionless figure of merit (ZT), defined as ZT = S 2 σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity, respectively. The reduction of thermal conductivity will improve heat-to-electricity energy conversion efficiency, enabling great advancement in thermoelectrics performance.…”

Synthesis and Magnon Thermal Transport Properties of Spin Ladder Sr14Cu24O41 Microstructures

“…scattering measurements have identified a steep triplet dispersion, suggesting much higher group velocities of magnons than those of the acoustic phonons. [18][19] The large and anisotropic  M provides an approach to enhance thermal transport in the complex structures, [20][21] which typically possess small lattice thermal conductivity ( L ) due to the presence of numerous optical phonon dispersions with low group velocities. [22] In addition, the large  M contribution is insensitive to magnetic fields up to 14 T since the magnon gap is much larger than the Zeeman energy.…”

Observation of suppressed diffuson and propagon thermal conductivity of hydrogenated amorphous silicon films

“…The thermal conductivities of the films were measured with TDTR, 28,36 a technique that has been thoroughly validated and extensively employed in the study of thermal conductivities of thin films, [37][38][39][40] nanocomposites, 41,42 bulk specimens, 43,44 and thermal conductance of interfaces. 45 Prior to thermal measurements, a thin layer of Al was deposited onto the sample surface as a Here, the H contribution to C a-Si:H is neglected at room temperature since the vibrational frequency of H atoms (~100 THz) is much higher than that of Si atoms (~10 THz).…”