Microstructure and electrical characterizations of CuO/Fe2O3 ceramics sintered by CO2 laser beams

Abstract

Layers of CuO/Fe2O3 mixture powders in a Cu/Fe molar ratio of 1:1 irradiated by continuous-wave CO2 laser beams in air transformed into face-centered-cubic Cu0.67Fe2.33O4 or CuFe5O8. The uneven or wavy surface with precursor residues after laser sintering was attributed to the intrinsic Gaussian beam profile and the temperature-induced tension gradient in the melt pool. The center valleys of the laser tracks exhibited larger faceted particles and more circular voids than those in the edge peaks. The nonstoichiometric phase transformation to Cu0.67Fe2.33O4 or CuFe5O8 grains and the formation of Cu2O along the grain boundaries can be seen in the X-ray diffraction patterns and transmission electron microscopic images. Microstructure characterizations via selected area electron diffraction revealed a preferred growth direction of <111> and coherent interfaces between the CO2 laser sintered Cu0.67Fe2.33O4 or CuFe5O8 grains and precipitated Cu2O due to a small lattice mismatch. The electrical voltage sweep measurements showed the resistivity in the range of 1.5 × 10−5–1.5 × 10−4 Ω ∙ m in the center valleys, indicating their potential applications on sensors, thermistor, and thermoelectric materials.