Contributed Speaker
Alexander Tselev
Quantification of Grain Boundary Thermal Resistance in Ceramics with SThM
D. Alikin¹, M.J. Pereira¹ , A. Abramov², E. Pashnina², M. Chuvakova², NV Lavrik³
,
W.
² Ural Federal University, Ekaterinburg, Russian Federation
³ Oak Ridge National Laboratory, Oak Ridge, USA
⁴ Technical University of Darmstadt, Darmstadt, Germany
Microstructure engineering is used to modify material thermal properties of importance in applications ranging from thermal management to energy harvesting. Understanding and controlling the impact of extended phonon-scattering defects, like grain boundaries, on thermal conductivity is essential for efficient material design, yet systematic studies are limited by the lack of adequate tools. This study demonstrates an approach for measuring grain boundary thermal resistance with passive-mode SThM by probing thermal wave propagation across grain boundaries. Thermal waves are generated by a microheater fabricated on the sample surface. SThM probing allows for point-by-point measurements of the thermal wave field and simplifies data analysis in comparison with optical methods. The method was applied to Nb-substituted SrTiO3 ceramics with an average grain size of approximately 5 μm. Using a linearized analytical model and numerical simulations, we quantified grain boundary thermal resistance by assessing changes in thermal wave amplitude and phase across grain boundaries. Detectability of approximately 2×10-8 K m2 W-1 was achieved, which makes this method directly applicable to chalcogenide-based thermoelectric materials, where typical grain boundary thermal resistances are relatively large. In turn, grain boundaries in oxides, with lower thermal resistances, require higher detectability. A major challenge in enhancing detectability is the probe's sensitivity to variations in the thermal resistance at the probe-sample contact, which stems from the relatively low thermal resistance between the probe and environment compared with a large thermal resistance at the probe-sample interface. In the future, these effects can be mitigated through improved signal-generation techniques. With account of the amount of material involved in the detection, our method's sensitivity is at least comparable to optical thermoreflectance methods.
AT acknowledges the 2021.03599.CEECIND contract through FCT (Portugal) and support by the European Union through the “ENSIGN” MSCA project. The work at the Univ. of Aveiro was supported by FCT/MEC (POCI-01-0145- FEDER-032117) and FCT/MCTES through CICECO (UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020).