Directional Thermal Transport in Inorganic Materials: Measurement Methods and Applications – A Case Study

Directional thermal transport, also referred to as anisotropic thermal conduction, is a key physical property governing performance and reliability in modern inorganic material systems. Unlike isotropic solids where heat spreads uniformly, many inorganic crystals, layered compounds, textured ceramics, and thin-film heterostructures exhibit strongly direction-dependent heat conduction due to anisotropic bonding, crystal symmetry, phonon dispersion, and interface-limited transport. Understanding and quantifying such directional heat flow is essential for advanced thermal management, high-power electronics, thermoelectric energy conversion, phase-change memory, and next-generation battery safety. This paper provides a comprehensive review of directional thermal transport mechanisms in inorganic materials and systematically evaluates widely used measurement techniques including time-domain and frequency-domain thermoreflectance, beam-offset thermoreflectance, 3ω methods, Raman thermometry, scanning thermal microscopy, transient plane source methods, and laser-flash analysis. A critical emphasis is placed on measurement reliability, model interpretation, and sources of uncertainty that commonly lead to inconsistency across reported results. Furthermore, this work includes a focused case study demonstrating how directional thermal transport can be resolved experimentally and interpreted through structure–transport correlations in an anisotropic inorganic material system, illustrating an application-driven approach for bridging fundamental thermal physics with device-level functionality. The review concludes by identifying key knowledge gaps and future research directions, particularly in standardization of anisotropic thermal measurements, anisotropy engineering via defect and interface design, and integration of directional heat transport materials into scalable device architectures.