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This study explores the correlation between thermal, electrical, and structural properties of metals, alloys, and single-crystal semiconductors using photothermal techniques, electrical methods, and X-ray diffraction. Polycrystalline metals (Al, Pt, Ti, Cu, AISI 1030 steel, α-brass) and semiconductors (Si, GaSb-Te) were systematically analyzed. Thermal diffusivity was measured using Frequency Domain Photoacoustic (FDPA), and thermal conductivity and volumetric heat capacity using the Thermal Relaxation Method (TRM). A thermal diffusivity image for a Si sample was taken to show the influence of mechanical damage on the thermal transport properties. The structural properties were determined using X-ray diffraction, while the electrical properties were evaluated using the Van der Pauw method. The results show a strong correlation between the thermal, electrical, and structural properties of the materials, specifically with respect to crystallite size and space group. The thermal conductivity is influenced by the crystallite size, while electrical conductivity varies due to extrinsic factors, especially for polycrystalline metals. These results suggest that the Wiedemann-Franz theory needs to be re-evaluated by considering both intrinsic and extrinsic influences on material behavior.