Insights on the Synthesis, Crystal and Electronic Structures, and Optical and Thermoelectric Properties of Sr_1–xSb_xHfSe₃ Orthorhombic Perovskite

Abstract

Single-phase polycrystalline powders of SrSb HfSe ( x = 0, 0.005, 0.01), a new member of the chalcogenide perovskites, were synthesized using a combination of high temperature solid-state reaction and mechanical alloying approaches. Structural analysis using single-crystal as well as powder X-ray diffraction revealed that the synthesized materials are isostructural with SrZrSe, crystallizing in the orthorhombic space group Pnma (#62) with lattice parameters a = 8.901(2) Å; b = 3.943(1) Å; c = 14.480(3) Å; and Z = 4 for the x = 0 composition. Thermal conductivity data of SrHfSe revealed low values ranging from 0.9 to 1.3 W m K from 300 to 700 K, which is further lowered to 0.77 W m K by doping with 1 mol % Sb for Sr. Electronic property measurements indicate that the compound is quite insulating with an electrical conductivity of 2.9 S/cm at 873 K, which was improved to 6.7 S/cm by 0.5 mol % Sb doping. Thermopower data revealed that SrHfSe is a p-type semiconductor with thermopower values reaching a maximum of 287 μV/K at 873 K for the 1.0 mol % Sb sample. The optical band gap of SrSb HfSe samples, as determined by density functional theory calculations and the diffuse reflectance method, is ∼1.00 eV and increases with Sb concentration to 1.15 eV. Careful analysis of the partial densities of states (PDOS) indicates that the band gap in SrHfSe is essentially determined by the Se-4p and Hf-5d orbitals with little to no contribution from Sr atoms. Typically, band edges of p- and d-character are a good indication of potentially strong absorption coefficient due to the high density of states of the localized p and d orbitals. This points to potential application of SrHfSe as absorbing layer in photovoltaic devices.

Chalcogenide Materials and Derivatives for Photovoltaic Applications

“…Different crystalline structures were observed, depending on the [Ba]/([Sr] + [Ba]) ratio: NH 4 CdCl 3 type for 0 < x < 0.68 values, biphasic mixtures of NH 4 CdCl 3 and CsNiCl 3 ‐type compounds for 0.68 < x < 1.0 values, and commensurate mismatched chain compound for the Ba 1.07 ZrSe 3 having a new orthorhombic needle‐like structure. Recently, Moroz et al have reported the synthesis of Sr 1–x Sb x HfSe 3 crystals having a needle‐like (orthorhombic) SrZrSe 3 type structure, using a combination of mechanical alloying and solid‐state reaction at elevated temperature (800 °C) methods. The doping of the SrHfSe 3 compound with Sb led to the increase of the bandgap (from 1.05 eV for x = 0 to 1.15 eV for x = 0.1).…”

Chalcogenide Perovskites: Tantalizing Prospects, Challenging Materials

“…ABSe 3 compounds with slightly smaller A cations, namely, SrZrSe 3 , [ 74 ] SrHfSe 3 , [ 82 ] and EuZrSe 3 , [ 94 ] were all grown in the NH 4 CdCl 3 ‐type phase. To the best of our knowledge, no phase transitions or alternative crystal structures have been reported for these compounds, in contrast to their sulfide relatives.…”

“…−1 . [ 121 ] ) From the experimental side, the synthesis was carried out at temperatures of 800 °C or higher, [ 74,82 ] and hence the difference in the entropy contribution to free energy must have been significant. This factor is ignored in standard energy calculations dealing with ground states (T = 0 K).…”

Realization of BaZrS3 chalcogenide perovskite thin films for optoelectronics

“…Meng et al [31] studied the BaZr1-xTixS3 alloy system, suggesting a limited concentration range before phase separation takes place. Optical and thermoelectric properties of SrHfSe3 and Sr1-xSbxHfSe3 were also studied [32]. Intense green luminescence characteristics were found in both undoped and heavily n-and p-doped SrHfS3 [28].…”