Structural, Surface-Chemical and Morphological Control of Effective Thermal Transport in La2O3-Modified ZnO Nanopowder Compacts

Abstract

Pristine ZnO and ZnO containing 1, 5, 10 and 20 wt.% nominal La2O3 were prepared by sol–gel-assisted chemical precipitation to investigate composition-dependent thermal transport in porous pressed-powder compacts. X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and field-emission scanning electron microscopy/energy-dispersive X-ray spectroscopy were integrated with transient plane source measurements to establish the structural, surface-chemical, morphological and thermophysical evolution of the composition series. XRD and Raman analyses confirmed preservation of the ZnO-dominant structural and vibrational framework, accompanied by La-bearing secondary environments and increasing local heterogeneity. FT-IR and XPS revealed hydroxylated and carbonate-sensitive oxygen environments associated with the La-containing surfaces, while FE-SEM/EDX showed hierarchical agglomerate structures and spatially distributed La throughout the modified powders. Effective thermal conductivity increased systematically from 1.43 to 2.30 W·m−1·K−1, corresponding to a 60.8% enhancement, while thermal diffusivity increased from 0.82 to 1.09 mm2 s−1. Mass-specific heat capacity increased from 0.678 to 0.738 J·g−1·K−1, and thermal effusiveness increased from approximately 1579 to 2203 W·s1ᐟ2·m−2·K−1. The accompanying increase in bulk density and evolution of agglomerate morphology indicate progressive improvement in compact consolidation and solid-contact continuity with increasing La2O3 content. Within this framework, La-containing surface chemistry contributes to the processing-driven development of agglomeration, packing and interparticle contact formation, thereby influencing the effective thermal architecture of the pressed bodies. The 20 wt.% composition exhibited the highest effective thermal conductivity within the investigated series. These results demonstrate that controlled modification of surface chemistry and particulate-network organization provides an effective route for enhancing thermal transport in porous ZnO-based compacts.