On thermal conductivity of amorphous niobium monoxide

Abstract

Thermal conductivity of NbO is studied experimentally and theoretically. Sputtered NbO samples, slightly overstoichiometric in oxygen, are x-ray amorphous with a combined NbO and NbO 2 short-range order, which is consistent with the quantum mechanical data. Upon annealing, NbO 2 crystallites form in the amorphous matrix due to an energetic preference of 44 meV atom −1 over NbO counterparts. The measured thermal conductivity at room temperature using time-domain thermoreflectance is 6.9 W m −1 K −1 , followed by a continuous increase due to electronic contributions, and it yields a total increase of 40 W m −1 K −1 at 650 K partly due to crystallisation. Phonon-phonon scattering can be induced by introducing Ni 0.75 Ta 0.25 O layers in NbO. These multilayers exhibit a thermal conductivity of 5.4 W m −1 K −1 at room temperature and a monotonic drop upon increasing temperature. It is thus feasible to modulate the high-temperature thermal conductivity of amorphous NbO by an order of magnitude. Hence, amorphous NbO may be of interest for thermoelectric devices, sensors and thermal insulation applications.

Optimization Design and Application of Niobium‐Based Materials in Electrochemical Energy Storage

“…Its Oh space group is 3 Nb atoms at the site 3(c) (0 1/2 1/2; 1/2 0 1/2; 1/2 1/2 0) and 3 O atoms at the site 3(d) (1/2 0 0; 0 1/2 0; 0 0 1/2), along with typical metal electrical behavior with resistivity about 20 μΩ cm À1 . [13] NbO, with lower thermal stability than that of Nb 2 O 5 , can be converted into pentavalent niobium under oxygen environment in the range of 300-500 C. [14] Although few researches on NbO, its application in energy storage system has been reported. Zhou [15] successfully synthesized NbO electrode material using Nb and Nb 2 O 5 as raw materials by high-temperature solid-phase method, and analyzed its energy storage mechanism via in situ X-ray diffraction (XRD) and a series of non-in situ characterization.…”

Mechanism of the Resistivity Switching Induced by the Joule Heating in Crystalline NbO2

“…[ 38 ] It has also been found that the amorphous phases of NbO$$_{2-x}$$ could exhibit a thermal conductivity in a wide range from less than 1 W m −1 K −1 to 7 W m −1 K −1 due to the mixture of NbO x and Nb 2 O$$_{5-x}$$. [ 39,40 ] The DFT calculation of thermal conductivity is challenging as well due to the phonon soft modes that emerge from the nature of the second order Peierls transition. [ 26,27 ] Nevertheless, since the phonon soft modes are highly damped, they do not contribute significantly to the thermal conductivity.…”

Mechanism of the resistivity switching in crystalline NbO$_2$

“…36 It has also been found that the amorphous phases of NbO 2−x could exhibit a thermal conductivity in a wide range from less than 1 W m −1 K −1 to 7 W m −1 K −1 due to the mixture of NbO x and Nb 2 O 5−x . 37,38 The DFT calculation of thermal conductivity is challenging as well due to the phonon soft modes that emerge from the nature of the second order Peierls transition. 25,26 Nevertheless, since the phonon soft modes are highly damped, they do not contribute significantly to the thermal conductivity.…”