Charge‐Compensated Compound Defects in Ga‐containing Thermoelectric Skutterudites

Abstract

Heavy doping changes an intrinsic semiconductor into a metallic conductor by the introduction of impurity states. However, Ga impurities in thermoelectric skutterudite CoSb3 with lattice voids provides an example to the contrary. Because of dual‐site occupancy of the single Ga impurity charge‐compensated compound defects are formed. By combining first‐principle calculations and experiments, we show that Ga atoms occupy both the void and Sb sites in CoSb3 and couple with each other. The donated electrons from the void‐filling Ga (GaVF) saturate the dangling bonds from the Sb‐substitutional Ga (GaSb). The stabilization of Ga impurity as a compound defect extends the region of skutterudite phase stability toward Ga0.15Co4Sb11.95 whereas the solid–solution region in other directions of the ternary phase diagram is much smaller. A proposed ternary phase diagram for Ga‐Co‐Sb is given. This compensated defect complex leads to a nearly intrinsic semiconductor with heavy Ga doping in CoSb3 and a much reduced lattice thermal conductivity (κL) which can also be attributed to the effective scattering of both the low‐ and high‐frequency lattice phonons by the dual‐site occupant Ga impurities. Such a system maintains a low carrier concentration and therefore high thermopower, and the thermoelectric figure of merit quickly increases to 0.7 at a Ga doping content as low as 0.1 per Co4Sb12 and low carrier concentrations on the order of 1019 cm−3.

Thermoelectric Properties of Group 13 Elements-Triple Filled Skutterudites: Nominal In<i>_x</i>Ga_0.02Tl_0.20Co₄Sb₁₂

“…23) Our group also has studied the TE properties of Ga-, In-, and Tl-filled skutterudites and confirmed that the group 13 elements filledskutterudites exhibit low ¬ lat and thereby relatively high ZT values. 2426) In particular, the maximum values of ZT of 0.9 and 0.7 at 600 K have been obtained for Tl-and In-filled skutterudites, respectively.…”

Defect-Controlled Electronic Structure and Phase Stability in Thermoelectric Skutterudite CoSb3

“…is the density of states of ideal host cell, and is the Fermi-Dirac distribution given by: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 13 (8) Following the procedure described above, the Fermi level (E F ) and free carriers can be determined by iteratively solving the overall charge neutrality requirement, as displayed in 17 The annealing temperature region of CoSb 3 is generally around 850 -1100 K. [14][15][16][17][18][19][20][21][22][23] The electron carrier concentration is found to be The total composition x of a phase with defects within an equilibrium set of atomic chemical potentials can be calculated by:…”

How thermoelectric properties of p-type Tl-filled skutterudites are improved

“…The unit cell contains two structural cages that can be filled by a variety of guest atoms such as rare earth elements, [4][5][6][7] alkaline earth metals, [8][9][10] alkali metals, 11,12 and group 13 elements. [13][14][15][16][17] When the guest atom denoted by R is incorporated into the cages, the general formula of the compounds, referred to as filled skutterudites, becomes RM 4 × 12 .…”