Thermal Conductivity of 2H and 2H3R Niobium Diselenide Polymorphs

Niobium diselenide(NbSe₂) is a two-dimensional van der Waals material whose 2H3R polymorph was discovered recently [1]. The 2H3R polymorph of NbSe₂ possesses a different stacking sequence when compared to the 2H polymorph due to the weak van der Waals bonding between the layers and therefore possesses different physical properties. Previous research has shown that difference in stacking sequence in two-dimensional materials can alter their electrical and thermal properties [1,2]. In this work the thermal conductivity of the 2H and 2H3R polymorphs of NbSe₂was measured and compared. The in-house T-bridge method was used in the measurement of thermal conductivity [3]. The T-bridge method measures the thermal conductivity of a sample through difference in heat conduction from a suspended heater to a heatsink. NbSe₂ samples of various thicknesses were prepared for both polymorphs. Measured thermal conductivity results showed that the 2H3R polymorph shows lower thermal conductivity compared to the 2H counterpart of similar thickness. Theoretical calculation was performed to study the cause of the difference in thermal conductivity and revealed that the lower thermal conductivity of the 2H3R polymorph was induced by the greater phonon-phonon scattering of the 2H3R polymorph than that of the 2H polymorph.<br/>[1] H. Moon, J. Kim, J. Bang, S. Hong, S. Youn, H. Shin, J.W. Roh, W. Shim, W. Lee, <i>Nano Energy</i> <b>78</b>, 105197 (2020)<br/>[2] P. Erhart, P. Hyldgaard, D. O. Lindroth, <i>Chemistry of Materials</i> <b>27</b>, 551-5518 (2015)<br/>[3] J. Kim, D. J. Seo, H. Park, H. Kim, H. J. Choi, W. Kim, <i>Review of Scientific Instruments</i> <b>88</b>, 054902 (2017)