Thermoelectric nanocrystalline YbCoSb laser prepared layers

Filled thermoelectric Yb_xCo₄Sb₁₂ layers were prepared by pulsed laser deposition method. The Yb_0.19Co₄Sb₁₂ target was fabricated by hot pressing. Various deposition conditions were tested: target - substrate distance d_T-S (4 or 6 cm), ambient argon pressure (from 0.5 to 13 Pa), laser repetition rate (from 3 to 10 Hz), substrate temperature (from 250 to 400 C) and laser fluence (in region from 0.8 to 5 J cm^-2). Film roughness was determined by mechanical profilometer and by AFM. For d_T-S = 4 cm we observed a deficit of Yb and surplus of Co. Sb was transferred from target to film roughly stoichiometrically (as measured by EDX). Films created at 0.8 J cm^-2 exhibited generally poor stoichiometry and mechanical properties. Optimal conditions and stoichiometric transport were found for d_T-S = 6 cm and 13 Pa of Ar. XRD shows that the films were nanocrystalline with CoSb₃ structure. Grain size was in the range of ∝ 50-80 nm. Temperature dependence of Seebeck coefficient and power factor was measured. Thermoelectric efficiency ZT ∝ 0.04-0.05 was measured at room temperature using Harman method. In dependence on layers quality, we calculated thermal conductivity λ ∝ 0.4-1.3 W K^-1 m^-1. (orig.)