Large thermopower in the antiferromagnetic semiconductor BaMn2Bi2

Abstract

We report electrical and thermal transport properties of Mn-based material BaMn 2 Bi 2 with ThCr 2 Si 2 structure. The resistivity of the antiferromagnetic BaMn 2 Bi 2 shows a metal-semiconductor transition at ∼ 80 K with decreasing temperature. Correspondingly, the thermopower S shows a peak at the same temperature, approaching 150 µV/K. With increasing temperature S decreases to about 125 µV/K at the room temperature. The magnetic field enhances the peak value to 210 µV/K. The Hall resistivity reveals an abrupt change of the carrier density close to the metal-semiconductor transition temperature.Thermoelectric materials with high Seebeck coefficient S (thermopower) have been attracting significant attention because of potential applications, particularly in waste heat recovery.1-4 High figure of merit (ZT=σS 2 T /κ, where σ and κ are the electrical and thermal conductivity, respectively) usually requires high thermopower. This raises considerable interest in exploratory synthesis of strongly correlated electron materials. Thermopower represents an electrical current entropy flow and therefore the charge/spin/orbital degrees of freedom might be manipulated for its enhancement, particularly around metal-insulator transitions. 5-8For example, giant thermopower and a record high thermoelectric power factor up towas observed in FeSb 2 with narrow energy gaps and correlated bands. 9-12Since the discovery of high temperature superconductivity in layered iron pnictide and iron chalcogenide compounds, the large diversity of the layered transitional metal pnictide compounds have been explored.13,14 In particular, doped AM 2 P n 2 (A=Ca, Sr, Ba or Eu, M =Fe, Mn, Rh or Co, and P n is pnictide or chalcogenide element) with ThCr 2 Si 2 (122-type) structure have been thoroughly investigated. Besides Fe-based high temperature superconductivity, high thermopower with metallic conduction was observed.15-17 Mn-based AM 2 P n 2 materials usually exhibit magnetic ground states with strong correlations.18-20 BaMn 2 As 2 and BaMn 2 Sb 2 are antiferromagnetic semiconductors due to the strong Hund's coupling and the stability of the half-filled d-shell of the Mn +2 ions. 18,19,21,22 Both were predicted to exhibit large Seebeck coefficient.19,21 Therefore, it is of interest to explore thermoelectric properties of isostructural and semiconducting BaMn 2 Bi 2 . 23Here we report electrical and thermal transport properties of Mn-based material BaMn 2 Bi 2 with ThCr 2 Si 2 structure.The resistivity of the antiferromagnetic BaMn 2 Bi 2 shows a metal-semiconductor transition at ∼ 80 K with decreasing temperature. Correspondingly, the thermopower S shows a peak at the same temperature and the value approaches 150 µV/K. With increasing temperature S decreases, but is still about 120 µV/K at the room temperature. The magnetic field enhances the peak value to 210 µV/K. The Hall resistivity reveals an abrupt change of the carrier density close to the metalsemiconductor transition temperature.Single crystals of BaMn 2 Bi 2 were grown using a high-t...

Crystal and Electronic Structure of Ternary Bismuthides BaTM1.8Bi2 (TM = Au, Ag) with a New Variation of the BaAu2Sb2 Structure Type

“…The first bismuthide with the ThCr 2 Si 2 type of structure, BaMn 2 Bi 2 , was reported only in 2013. It displays antiferromagnetic and thermoelectric properties, and, with the partial substitution of barium for potassium, it demonstrates a transition to a superconducting state [1,8,9]. Recently, we have presented several compounds of the ATM 2 Bi 2 (A = K, Rb, Cs, TM = Zn, Cd) series crystallizing in the ThCr 2 Si 2 structure type, in which a certain electron deficiency and the presence of Bi•••Bi interaction between neighboring layers were observed [10].…”

Thermopower of the electron-doped manganese pnictide LaMnAsO

“…A class of strongly correlated materials for which experiments have repeatedly reported high thermopowers (Seebeck coefficients) are the manganese pnictides [10][11][12][13][14][15][16][17][18]. We focus on one example out of this material class, electron-doped LaMnAsO, where doping can be accomplished experimentally by a fractional replacement of the O atoms with F [18; 19].…”

Isovalent Ca and Ba substitutions in thermoelectric layer-structured oxyselenide Sr2CoO2Cu2Se2

“…Ternary ThCr 2 Si 2 -type compounds have a single layer of cations sandwiched in between two anti-fluorite layers [13]. Among them the AMn 2 Pn 2 (A = Ba, Sr, Ca; Pn: pnictogen) phases are semiconductors with decent thermopower induced by magnetic ordering [14]. Most of the ACu 2 Ch 2 (Ch: chalcogen; A = alkaline or alkaline earth element when Ch = S, or A = Tl when Ch = Se) phases, on the other hand, exhibit metallic conduction and poor Seebeck coefficient near or above room temperature, except the doped BaCu 2 Se 2 phase [15].…”