Advancing thermoelectrics by suppressing deep-level defects in Pb-doped AgCrSe_(2) alloys

AgCrSe2-based compounds have attracted much attention as an environmentally friendly thermoelectric material in recent years due to the intriguing liquid-like properties.However,the ultra-low carrier concentration and the high Ag_(Cr)deep-level defects limit the overall thermoelectric performance.Here,we successfully introduced Pb into Ag-deficient Ag_(0.97)CrSe_(2) alloys to tune the carrier concentration across a broad temperature range.The Pb^(2+) as an acceptor dopant preferentially occupies Cr sites,boosting the hole carrier concentration to 1.77×10^(19) cm^(-3) at room temperature.Furthermore,the Pb strongly inhibits the creation of intrinsic Ag_(Cr) defects,weakens the increased thermal excited ionization with the increasing temperature and slowed the rising trend of the carrier concentration.The designed carrier concentration matches the theoretically predicted optimized one over the entire temperature range,leading to a remarkable enhancement in power factor,especially the maximum power factor of ~500 μW·m^(-1)·K^(-2) at 750 K is superior to most previous results.Additionally,the abundant point defects promote phonon scattering,thus reducing the lattice thermal conductivity.As a result,the maximum figure of merit zT(~0.51 at 750 K) is achieved in Ag_(0.97)Cr_(0.995)Pb_(0.005)Se_(2).This work confirms the feasibility of manipulating deep-level defects to achieve temperature-dependent optimal carrier concentration and provides a valuable guidance for other thermoelectric materials.

Annealing engineering induced high thermoelectric performance in Yb-filled CoSb_(3) skutterudites

The great pressure of energy shortage has made CoSb_(3) materials with excellent mechanical stability in the mid-temperature region favored for the integration of thermoelectric devices.However,their ex-cessive lattice thermal conductivity and poor Seebeck coefficient lead to low energy conversion effi-ciency.Filling Yb into the lattice void to optimize the band structure and regulate the chemical po-tential is an indispensable means for improving the thermoelectric properties of CoSb_(3)-based materials,while the phase structure and thermoelectric properties vary with the preparation process.This motivates the current work to focus on the influence of annealing temperature on the microstructure and thermoelectric properties of Yb-filled CoSb_(3).Experimental analysis and theoretical model eluci-dated that an increase in annealing temperature can optimize the Yb filling fraction,which simulta-neously manipulates the band structure as well as chemical potential,resulting in an excellent electrical property.Furthermore,the phase and microstructure characterization clarify that the annealing temperature can effectively affect the grain size.The complex grain boundary induced by grain refinement,more filled Yb atoms and precipitates strongly scatter wide-frequency phonons,significantly suppressing the lattice thermal conductivity.As a result,a superior dimensionless figure of merit(ZT)value of~1.33 at 823 K and an average ZTave of~0.9(323-823 K)were achieved in the Ybo.4Co4Sb12 sample annealed at 923 K,and the calculated conversion efficiency could reach~13%.This work pro-vides a unique paradigm to improve thermoelectrics in the filled CoSb_(3)-based skutterudites by annealing engineering.