Enhanced thermoelectric performance of n-type transformable AgBiSe2 polymorphs by indium doping

Abstract

We demonstrate the improved thermoelectric properties of n-type lead-free transformable AgBiSe2 polymorphs by indium doping on silver sites. X-ray diffraction analysis suggests that complete solid solutions are well formed up to [In] = 0.02. Electrical conductivity and Seebeck coefficient behave in a routinely opposite manner due to the dominant role of the carrier concentration adjusted by the localized indium impurity levels, as also suggested by our density functional theory (DFT) calculations. As indium concentration increases, we observe a drastic variation of the thermoelectric transport properties with temperature, in the range of 450 to 580 K. By performing the isothermal electrical measurements, we attribute this interesting behavior to the ongoing α to β phase transformation process. The In 5s lone pair electrons, as indicated from our DFT calculations, increase the anharmonicity of the chemical bonds and enhance the phonon-phonon scattering. This, together with the introduced InAg.. point defects, further brings down the lattice thermal conductivity. The maximum thermoelectric figure of merit ZT is achieved at 773 K and increases from 0.3 for pristine AgBiSe2 to 0.7 for an optimal [In] = 0.015 doping, a more than two times enhancement.

Comparing the role of annealing on the transport properties of polymorphous AgBiSe2 and monophase AgSbSe2

“…Therefore, thermoelectric materials with intrinsically low thermal conductivity are particularly appealing, among which I-V-VI 2 compounds (where I ¼ Cu, Ag or alkali metal; V ¼ Sb, Bi; and VI ¼ S, Se, Te) emerge as new candidates. [12][13][14][15][16][17][18][19][20][21] The intrinsically low lattice thermal conductivity (k l ) of I-V-VI 2 compounds arises from the strong lattice anharmonicity that is believed to associate with the lone pair electrons (s electrons) on the group V atoms. [22][23][24] Among numerous I-V-VI 2 compounds, AgSbTe 2 is widely studied due to the low thermal conductivity and high Seebeck coefficient.…”

Thermoelectric optimization of AgBiSe2 by defect engineering for room-temperature applications

“…We then calculate the electrical conductivity s/τ of the pristine and VAg AgBiSe2 systems using the BTE. By matching these calculated results with the experimentally measured electrical conductivities [25] of the corresponding systems at the same carrier concentration and temperature, we can obtain the constant number C0. Since we focus on the thermoelectric properties at the low temperature region, we choose the calculated and experimental data at [300 K, 1.96 ×10 20 cm -3 ] and [300 K, 0.93 ×10 20 cm -3 ] for AgBiSe2 and VAg, respectively.…”

“…Since the BTE calculated electrical conductivity s/τ includes the hardly defined carrier scattering relaxation time τ, we are going to use the experimentally measured electrical conductivity data from Ref. [25] to obtain its value. The relaxation time (τ) takes into account the contributions from both acoustic and optical phonons.…”

“…AgBiSe2 crystallizes in a hexagonal structure at room temperature. It undergoes two structural phase transitions [24][25][26][27][28][29] at a higher temperature, ~460 K (hexagonal to rhombohedral) and ~580 K (rhombohedral to cubic). AgBiSe2 has the intrinsic low lattice thermal conductivity (0.45 W/mK at 300 K [30,31]).…”

Influence of the temperature and composition on the crystal structure of the AgBiSe2‐AgBiS2 system

“…Therefore, the thermoelectric figure of merit ZT, defined as (with S the Seebeck coefficient, σ the electrical conductivity, λ the thermal conductivity and T the absolute temperature), which constitutes the main criterion to evaluate the performances of thermoelectric materials, reaches promising values upon relevant doping. For example, ZT = 1 has been observed in Nb‐doped AgBiSe 2 or Cl‐doped AgBiSeS , ZT = 0.9 in Cl‐doped AgBiSe 2 , or ZT = 0.7 in In‐doped AgBiSe 2 around 500–550°C.…”