Zintl Compounds Research Articles

Bonding Interactions Can Drive Topological Phase Transitions in a Zintl Antiferromagnetic Insulator

AbstractWhile ∼30% of materials are reported to be topological, topological insulators are rare. Magnetic topological insulators (MTI) are even harder to find. Identifying crystallographic features that can host the coexistence of a topological insulating phase with magnetic order is vital for finding intrinsic MTI materials. Thus far, most materials that are investigated for the determination of an MTI are some combination of known topological insulators with a magnetic ion such as MnBi2Te4. Motivated by the recent success of EuIn2As2, the role of chemical pressure on topologically trivial insulator is investigated, Eu5In2Sb6 via Ga substitution. Eu5Ga2Sb6 is predicted to be topological but is synthetically difficult to stabilize. The intermediate compositions between Eu5In2Sb6 and Eu5Ga2Sb6 are observed through theoretical works to explore a topological phase transition and band inversion mechanism. The band inversion mechanism is attributed to changes in Eu–Sb hybridization as Ga is substituted for In due to chemical pressure. Eu5In4/3Ga2/3Sb6 is also synthesized, the highest Ga concentration in Eu5In2‐xGaxSb6, and report the thermodynamic, magnetic, transport, and Hall properties. Overall, the work paints a picture of a possible MTI via band engineering and explains why Eu‐based Zintl compounds are suitable for the co‐existence of magnetism and topology.

Enhancing Thermoelectric Performance of Mg3Sb2 Through Substitutional Doping: Sustainable Energy Solutions via First-Principles Calculations

Mg3Sb2-based materials, part of the Zintl compound family, are known for their low thermal conductivity but face challenges in thermoelectric applications due to their low energy conversion efficiency. This study addressed these limitations through first-principles calculations using the CASTEP module in Materials Studio 8.0, aiming to enhance the thermoelectric performance of Mg3Sb2 via strategic doping. Density functional theory (DFT) calculations were performed to analyze electronic properties, including band structure and density of states (D.O.S.), providing insights into the influence of various dopants. The semiclassical Boltzmann transport theory, implemented in BoltzTrap (version 1.2.5), was used to evaluate key thermoelectric properties such as the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and electronic figure of merit (eZT). The results indicate that doping significantly improved the thermoelectric properties of Mg3Sb2, facilitating a transition from p-type to n-type behavior. Bi doping reduced the band gap from 0.401 eV to 0.144 eV, increasing carrier concentration and mobility, resulting in an electrical conductivity of 1.66 × 106 S/m and an eZT of 0.757. Ge doping increased the Seebeck coefficient to −392.1 μV/K at 300 K and reduced the band gap to 0.09 eV, achieving an electronic ZT of 0.859 with low thermal conductivity (11 W/mK). Si doping enhanced stability and achieved an electrical conductivity of 1.627 × 106 S/m with an electronic thermal conductivity of 11.3 W/mK, improving thermoelectric performance. These findings established the potential of doped Mg3Sb2 as a highly efficient thermoelectric material, paving the way for future research and applications in sustainable energy solutions.

The mysterious magnetic ground state of Ba14MnBi11 is likely self-doped and altermagnetic

Magnetism in the Zintl compound Ba14MnBi11 is rather poorly understood. Experimental claims are largely inconsistent with ab initio calculations, much beyond typical errors of the latter. We revisit this old problem, assuming that the root of the problem may be in nonstoichiometry of existing samples. Our key finding is that the magnetic ground state is indeed very susceptible to charge doping (band filling). Calculations for stoichiometric Ba14MnBi11 give a rather stable ferromagnetic metallic state, in agreement with previous publications. However, by adding exactly one electron per Mn, the system becomes semiconducting as expected, and becomes weakly antiferromagnetic (AF). On the other hand, upon small amount of hole doping, the system transitions to a special type of AF state known as altermagnetism. Furthermore, hole and electron doping-induced phase transitions result from different underlying mechanisms, influencing different exchange pathways. We propose that the inconsistency between experiment and theory is not a failure of the latter, but results from a nontrivial ramification of nonstoichiometry. The possibility of doping-stabilized altermagnetism is exciting.

Realizing Ultrahigh Conversion Efficiency of ≈9.0% in YbCd2Sb2/Mg3Sb2 Zintl Module for Thermoelectric Power Generation.

Recently, YbCd2Sb2-based Zintl compounds have been widely investigated owing to their extraordinary thermoelectric (TE) performance. However, its p orbitals of anions that determined the valence band structure are split due to crystal field splitting that provides a good platform for band manipulation by doping/alloying and, more importantly, the YbCd2Sb2-based device has yet to be reported. In this work, single-phase YbCd1.5Zn0.5Sb2 is successfully obtained through precise chemical composition control. Then, YbMg2Sb2-alloying increases the cationic vacancy defect formation energy and further optimizes carrier concentration. Moreover, the band structure of YbCd1.5Zn0.5Sb2 is subtly manipulated, and the underlying mechanism is experimentally explored. Combined with the reduced lattice thermal conductivity, a high peak ZT value of ∼1.43 at 700K is obtained for YbCd1.425Zn0.475Mg0.1Sb2. Subsequently, choosing Fe90Sb10 as the diffusion barrier layer and adopting the transient liquid phase bonding technique, for the first time, it is demonstrated that YbCd2Sb2/Mg3(Sb, Bi)2 TE module with an ultrahigh conversion efficiency of ≈9.0% at a heat difference of 430K. More importantly, this module displays good thermal stability. This work paves the way for YbCd2Sb2 materials and devices in mid-temperature heat recovery.

Ultralow Lattice Thermal Conductivity of Zintl‐Phase CaAgSb Induced by Interface and Superlattice Scattering

Zintl phases attract extensive attention due to the characteristic of “electron‐crystal, phonon glass”. In this work, an ultralow lattice thermal conductivity ≈0.59 W m−1 K−1 at 300 K and ≈0.3 W m−1 K−1 at 623 K is obtained in CaAgSb Zintl phase, which is much lower than that of other well‐known Zintl compounds. The origin of this ultralow lattice thermal conductivity is explored through first‐principles calculations and Cs‐corrected scanning transmission electron microscopy. Theoretical phonon calculations provide evidence for complex phonon characteristics such as avoided‐crossing effect and low‐frequency flat band that favor the low lattice thermal conductivity. Moreover, subsequent microstructure results reveal abundant structural defects created in the CaAgSb sample, including superlattice structure and interface structure, which further contribute to the ultralow lattice thermal conductivity.

First-principles study of optoelectronic and thermoelectric aspects of novel zintl phase SrAg2X2 (X = S, Se, Te) alloys for green energy applications

This work comprehensively investigates the solar energy harvesting and thermoelectric capabilities of innovative Zintl phase SrAg2X2 (X = S, Se, Te) alloys. Herein, the analysis of the structural, optoelectronic, and thermoelectric characteristics of Zintl SrAg2X2 (X = S, Se, Te) compounds has been conducted utilizing the WIEN2k code. The formation energy has been evaluated to elaborate the thermodynamic stability of Zintl compounds. The materials demonstrate characteristics of semiconductors, with anticipated band gap values of 1.78 eV for SrAg2S2, 1.63 eV for SrAg2Se2, and 1.50 eV for SrAg2Te2. The optical characteristics have been examined to assess the potential use of these phases in optoelectronic and photovoltaic systems. The standard Boltzmann transport theory has been used to analyze thermoelectric parameters concerning temperature and chemical potential. Thermoelectric features have also verified the p-type characteristics of these semiconductors. Considerably higher predicted values of the power factor and higher figure of merit demonstrate the capability of thermal energy conversion. Consequently, these outstanding optoelectronic and thermoelectric aspects values indicate that this class of materials may be highly suitable for use in solar and thermoelectric systems.

A theoretical investigation on the structure stability, electronic structures, optical properties, and transport properties of Zintl compounds CsZn4P3 and CsZn4As3

The present study investigates the structure stability, electronic structures, and optical properties of Zintl compounds CsZn4P3 and CsZn4As3 by first-principles calculations. An assessment of the phonon dispersion curves and elastic constants indicate both dynamic and mechanical stability for the both compounds. By employing the HSE06 hybrid functional, both compounds display direct bandgap with widths of 0.93 eV for CsZn4P3 and 0.66 eV for CsZn4As3. Furthermore, an analysis of the dielectric constant, refractive index, extinction coefficient, and energy loss as functions of photon energy is conducted to study the optical properties. Based on the semi-classical Boltzmann transport theory and the Slack's equation, a large Seebeck coefficient and minimum lattice thermal conductivity are obtained for CsZn4As3, which result in a figure of merit value of 0.79 at 700 K. These findings underscore the potential of CsZn4As3 as a promising candidate for future research and development in the realm of thermoelectric materials.

Large Number of Direct or Pseudo-Direct Band Gap Semiconductors among A3TrPn2 Compounds with A = Li, Na, K, Rb, Cs; Tr = Al, Ga, In; Pn = P, As.

Due to the high impact of semiconductors with respect to many applications for electronics and energy transformation, the search for new compounds and a deep understanding of the structure-property relationship in such materials has a high priority. Electron-precise Zintl compounds of the composition A3TrPn2 (A = Li - Cs, Tr = Al - In, Pn = P, As) have been reported for 22 possible element combinations and show a large variety of different crystal structures comprising zero-, one-, two- and three-dimensional polyanionic substructures. From Li to Cs, the compounds systematically lower the complexity of the anionic structure. For an insight into possible crystal-structure band-structure relations for all compounds (experimentally known or predicted), their band structures, density of states and crystal orbital Hamilton populations were calculated on a basis of DFT/PBE0 and SVP/TZVP basis sets. All but three (Na3AlP2, Na3GaP2 and Na3AlAs2) compounds show direct or pseudo-direct band gaps. Indirect band gaps seem to be linked to one specific structure type, but only for Al and Ga compounds. Arsenides show smaller band gaps than phosphides due to weaker Tr-As bonds. The bonding situation was confirmed by a Mullikan analysis, and most states close to the Fermi level were assigned to non-bonding orbitals.

An ab initio analysis of the electronic, optical, and thermoelectric characteristics of the Zintl phase CsGaSb2

We present and analyze the findings of a comprehensive ab initio computation that examines the electronic, optical, and thermoelectric characteristics of a recently synthesized Zintl compound known as CsGaSb2. The electronic and optical characteristics were examined using the DFT-based FP-L/APW+loapproach. Toaddress the exchange–correlation effects, we employed the GGA-PBEsol and TB-mBJ approaches.The CsGaSb2 semiconductor exhibits an indirect bandgap of 0.695 eV when analyzed with the GGA-PBEsol approach, and a bandgap of 1.254 eV when analyzed with the TB-mBJ approach.The PDOS diagrams were used to discover the origins of the electronic states that make up the energy bands. The charge density study reveals that the Ga-Sb link within the [GaSb2] block is mostly governed by a covalent character, whereas the cation Cs+ and polyanion [MSb2]−bonding is predominantly ionic. The frequency dependence of macroscopic linear optical coefficients was evaluated over a broad range of photon energies from 0 to 25 eV. The thermoelectric characteristics were investigated via the Boltzmann kinetic transport theoryassuming a constant relaxation time.The compound’s figure of merit at a temperature of 900 K is roughly 0.8.

Thermoelectric properties of zintl antimonite compound YbCd2-xZnxSb2 prepared under microwave solid-state irradiation

We herein introduce a microwave-assisted solid state technique to synthesize zintl compounds YbCd2-xZnxSb2 (0.0 ≤ x ≤ 2.0) in short time of 10 min by utilizing an active carbon as a susceptor material. Here, we report an energy-saving preparation route using a domestic microwave oven. A microwave susceptor material rapidly heats the elemental starting materials inside an evacuated quartz ampoule resulting in near single phase compounds. By studying the crystal structure using X-Ray diffraction (XRD) and SEM-EDS, the hexagonal crystal structures of the prepared samples were identified. Thermoelectric characterizations have been performed for all obtained samples and among them the compound YbCd1.6Zn0.4Sb2 is found as the best one because it has Seebeck coefficient of −22.68 μV/k, and power factor of 8.20 μWcm−1k−2 at 523 K with carrier concentration of 3.04 × 1021 cm−3 at 300 K.

Investigation of pressure-driven superconductivity in TlInTe2: an ab initio study

The Zintl compound TlInTe2 is an intriguing material because of its outstanding thermoelectric properties at ambient pressure. Interestingly, it has recently been found that TlInTe2 exhibits a V-shape dependence of the superconducting critical temperature (T c) under increasing pressure, which has been linked to the reversed behavior of the Raman active Ag phonon mode and anharmonic effects. In this study, we have performed first-principles calculations of the electron-phonon interactions and the superconducting properties of TlInTe2 in order to understand this unusual pressure-induced response. In contrast to experiment, we find a dome-shaped pressure-induced dependence of T c with a maximum value of 0.23 K at 18 GPa, significantly lower than the experimental results. Electron doping has the potential to adjust the T c to fall within the experimental range, but it necessitates considerably high levels of doping. Furthermore, our analysis of the phonon spectra and phonon lifetimes, including anharmonic effects, show that anharmonicity is unlikely to influence the superconducting properties of TlInTe2. It remains an open question whether there is indeed an unusual V-shape T c dependence with pressure or whether the phonon-mediated theory of superconductivity used here breaks down in this system.

First principles investigations of optoelectronic and thermoelectric properties of novel BaMg2X2 (X = P, As, Sb) alloys for renewable energy applications

Zintl phase compounds are emerging candidates for solar cells due to their unique electronic structure and favorable optoelectronic characteristics. In the present communication, we have studied the structural, electronic, optical, and transport properties of BaMg2X2 (X = P, As, Sb) Zintl compounds. The computation of formation energy and analysis of phonon dispersion spectra confirm their favorable formation and dynamic stability. Employing modified Becke-Johnson (mBJ) potential, we elucidate the band structure for BaMg2P2, BaMg2As2, and BaMg2Sb2, revealing direct band gaps of 1.80, 1.65, and 1.35 eV, respectively. Examination of DOS spectra provides better insight regarding the contribution of 6 s-Ba, 3 s-Mg, and (3p-5p)-P/As/Sb states in forming valence and conduction bands. The scrutiny of the optical characteristics indicates compelling light absorption in the visible region, suggesting promising prospects for optoelectronic applications. Thermoelectric characteristics are evaluated using classical Boltzmann transport theory. Notably, large figure of merit values of 0.99, 0.97 and 0.95 for BaMg2P2, BaMg2As2, and BaMg2Sb2, respectively, have been observed at room temperature. These exceptional optoelectronic characteristics, coupled with outstanding ZT values, suggest the potential suitability of these compositions for solar cells and thermoelectric device applications.

Pressure‐Induced Superconductivity and Structure Phase Transition in SnAs‐Based Zintl Compound SrSn2As2

AbstractLayered SnAs‐based Zintl compounds exhibit a distinctive electronic structure, igniting extensive research efforts in areas of superconductivity, topological insulators, and quantum magnetism. In this paper, the crystal structures and electronic properties of the Zintl compound SrSn2As2 upon compression are systematically investigated. Pressure‐induced superconductivity is observed in SrSn2As2 with a nonmonotonic evolution of superconducting transition temperature Tc. Theoretical calculations together with high‐pressure synchrotron X‐ray diffraction and Raman spectroscopy have identified that SrSn2As2 undergoes a structural transformation from a rhombohedral Rm phase to the monoclinic C2/m phase. Beyond 28.3 GPa, Tc is suppressed due to a reduction of the density of state (DOS) at the Fermi level. The discovery of pressure‐induced superconductivity, accompanied by structural transitions in SrSn2As2, greatly expands the physical properties of layered SnAs‐based compounds and provides new ground states upon compression.

First-principles investigation of structural, electronic and thermoelectric properties of SmMg2X2 (X = P, As, Sb, Bi) zintl compounds

Structure complexity, adequate electronic character and congenital lower thermal conductivity of zintl phases result in designing thermoelectrics of tremendous efficiency. Such qualities of zintl phases embolden us to present a detailed study of SmMg2X2 (X = P, As, Sb, Bi) zintl compounds by first principles. The structural characteristics fit well with the existing data. Electronic properties of titled compounds are scrutinized by adopting PBE-GGA, TB-mBJ and hybrid (YS-PBE0) potentials. The band structure calculations through TB-mBJ and hybrid (YS-PBE0) proclaim the semiconducting behavior of compounds and there is a shrinkage of band gap by changing X anion from P to Bi. The density of states (DOS) calculation reveals that there is a major contribution of Sm-f states and Mg atom in valence band while in conduction band, the prominent role is offered by Sm-d states and p states of X anion. Similarly, the temperature-dependent thermoelectric properties are scrutinized by using BoltzTraP2 code embedded within WIEN2k software for with and without spin–orbit coupling (SOC) and also through hybrid (YS-PBE0) functional. SOC, but even more hybrid functional, has been shown to have a significant effect on the transport behavior. Optimized values of carriers’ concentration are achieved which subsidize thermoelectric parameters like power factor (PF), Seebeck coefficient ([Formula: see text] and thermoelectric figure of merit (ZT) at elevated temperature. The compounds show excellent thermoelectric performance in the studied temperature range.

Investigation of optoelectronic and thermoelectric properties of novel BaCd2X2 (X = P, As, Sb) Zintl-phase for energy harvesting applications

The quest for new Zintl phases with promising thermoelectric properties has gained significant momentum recognitions to the precision of computational predictions. Our study presents an in-depth investigation of fundamental characteristics like structural, optoelectronic, optical, and transport aspects of BaCd2X2 (X = P, As, Sb) Zintl compounds. The stability of all compounds is firmly established through their optimized negative (-ve) formation energies and phonon dispersion spectra. Our findings affirm their robust structural integrity. Notably, we observe a semiconductor nature in these compounds, with calculated bandgap values of 1.35 eV for BaCd2P2, 0.85 eV for BaCd2As2, and 0.23 eV for BaCd2Sb2. Probing into optical properties, we uncover their potential utility in optoelectronic devices, as indicated by the optical response of these phases. We employ semi-classical Boltzmann theory, executed via BoltzTraP code, to explore their thermal behavior. Impressively higher values of Seebeck are attained, both at RT and elevated temperatures. Furthermore, the power factor exhibits an increasing trend with increasing temperature. Crucially, the analysis of the figure of merit (ZT) reveals promising values, 0.90, 0.81, and 0.72 for BaCd2X2 (X = P, As, Sb) at 300 K, respectively. These favorable optical and thermoelectric characteristics position these phases as attractive candidates for applications in optoelectronics and thermoelectric systems.

Thermoelectric Properties of Zn-Doped YbMg1.85-xZnxBi1.98.

Bi-based YbMg2Bi1.98 Zintl compounds represent promising thermoelectric materials. Precise composition and appropriate doping are of great importance for this complex semiconductor. Here, the influence of Zn substitution for Mg on the microstructure and thermoelectric properties of p-type YbMg1.85-xZnxBi1.98 (x = 0, 0.05, 0.08, 0.13, 0.23) was investigated. Polycrystalline samples were prepared using induction melting and densified with spark plasma sintering. X-ray diffraction confirmed that the major phase of the samples possesses the trigonal CaAl2Si2-type crystal structure, and SEM/EDS indicated the presence of minor secondary phases. The electrical conductivity increases and the lattice thermal conductivity decreases with more Zn doping in YbMg1.85-xZnxBi1.98, whereas the Seebeck coefficient has a large reduction. The band gap decreases with increasing Zn concentration and leads to bipolar conduction, resulting in an increase in the thermal conductivity at higher temperatures. Figure of merit ZT values of 0.51 and 0.49 were found for the samples with x = 0 and 0.05 at 773 K, respectively. The maximum amount of Zn doping is suggested to be less than x = 0.1.

The Substitution of Rare-Earth Gd in BaScCuTe3 Realizing the Band Degeneracy and the Point-Defect Scattering toward Enhanced Thermoelectric Performance.

Zintl compounds have continuously received significant attention, primarily due to their structural characteristics that align with the properties of the electron crystal and phonon glass. In this study, the crystal structure and thermoelectric properties of the quaternary Zintl chalcogenide BaScCuTe3 are investigated. The band structure calculations for BaScCuTe3 reveal a slight energy split of 0.08 eV between the second valence band and the valence band maximum, suggesting the presence of multiband-transport behaviors. Substitution of rare earth Gd for Sc is conducted, which significantly increases the hole concentration from 4.1 × 1019 cm-3 to 8.2 × 1019 cm-3 at room temperature. Meanwhile, the Seebeck coefficient increases because of the participation of the second valence band. A maximum power factor of 6.56 μW/cm·K2 at 773 K is obtained, which is 72% higher than that of the pristine sample. Moreover, the lattice thermal conductivity decreases from 0.57 W/m·K for BaScCuTe3 to 0.48 W/m·K for BaSc0.97Gd0.03CuTe3 at 773 K, owing to the introduction of point-defect scattering. As a result, there is a noteworthy improvement in the thermoelectric figure of merit zT, increasing from 0.44 for the undoped sample to 0.85 for BaSc0.98Gd0.02CuTe3. Considering these findings, BaScCuTe3 exhibits great potential and holds promise for further investigation in the field of thermoelectric materials.

Alloying-Induced Structural Transition in the Promising Thermoelectric Compound CaAgSb.

AMX Zintl compounds, crystallizing in several closely related layered structures, have recently garnered attention due to their exciting thermoelectric properties. In this study, we show that orthorhombic CaAgSb can be alloyed with hexagonal CaAgBi to achieve a solid solution with a structural transformation at x ∼ 0.8. This transition can be seen as a switch from three-dimensional (3D) to two-dimensional (2D) covalent bonding in which the interlayer M-X bond distances expand while the in-plane M-X distances contract. Measurements of the elastic moduli reveal that CaAgSb1-xBix becomes softer with increasing Bi content, with the exception of a steplike 10% stiffening observed at the 3D-to-2D phase transition. Thermoelectric transport measurements reveal promising Hall mobility and a peak zT of 0.47 at 620 K for intrinsic CaAgSb, which is higher than those in previous reports for unmodified CaAgSb. However, alloying with Bi was found to increase the hole concentration beyond the optimal value, effectively lowering the zT. Interestingly, analysis of the thermal conductivity and electrical conductivity suggests that the Bi-rich alloys are low Lorenz-number (L) materials, with estimated values of L well below the nondegenerate limit of L = 1.5 × 10-8 W Ω K-2, in spite of the metallic-like transport properties. A low Lorenz number decouples lattice and electronic thermal conductivities, providing greater flexibility for enhancing thermoelectric properties.

Effects of Pd atom vibration in the Sr–Te octahedral interstitial space in Zintl compound SrPdTe on lattice anharmonicity and thermoelectric properties

Based on first-principles calculations, the current study deeply explores the thermoelectric properties of the Zintl compound SrPdTe. We found that the anharmonic vibration of Pd atoms plays an important role in the quartic anharmonic effect and the temperature dependence of the thermal conductivity. In the crystalline structure, Sr atoms form octahedra with eight surrounding Te atoms, while Pd atoms are located in the gaps between the octahedra. This structure makes the strong atomic mean square displacement of Pd atoms the main factor leading to the ultralow thermal conductivity. The study also reveals the effects of phonon frequency renormalization and four-phonon scattering on heat transfer performance. Even considering the spin–orbit coupling effect, multiple secondary valence band tops maintain the power factor of the material at high temperatures, providing a potential opportunity for achieving excellent thermoelectric performance.

First principles investigation on optoelectronic and thermoelectric response of nitrides cadmium novel zintl compounds AB2C2 (A=Mg, Ca, Sr, Ba; B = Cd and C= N)

Novel materials for high efficiency advance devices are critical to investigate. Zintl compounds are widely explored in the recent years because of their direct narrow band gaps, higher optical conductivity and figure of merit required for optimal-optoelectronic and thermoelectric response respectively. Thus, in the current study, the structural, electronic, optical and thermoelectric properties of nitrides cadmium novel Zintl compounds AB2C2 (A=Mg, Ca, Sr, Ba; B=Cd and C= N) having trigonal structure are studied by full potential linearized augmented plane wave method based on density functional and Boltzmann transport theory. The main objective of this project is to provide novel thermo electrical data on Cd-based Zintl compounds, such as nitride cadmium-based compounds. To get the desire results, the exchange correlations with generalized gradient approximation were used to obtain the ground state structure parameters in these compounds. The computed lattice parameters and c/a -ratio increase from the top to down while the bulk-modulus B(GPa) decreases from top to bottom. The modified versions of the Beck-Johnson potential (TB-mBJ) predict that CaCd2N2, SrCd2N2, BaCd2N2 and MgCd2N2 compounds are semiconductors with narrow band gap of 0.18 eV, 0.21 eV, 0.84 eV and 0.07 eV respectively. Based on the optical properties a deep analysis of dielectric constant, refractive index, reflectivity and optical conductivity were carried. Across the entire temperature range, all the compounds exhibit a positive Seebeck coefficient, indicating P-type conduction. The direct energy band gap nature of these compounds with high conductivity in the visible region shows their suitability for optical applications. Also, the figure of merit of these compounds is close to unity which also speaks about the high efficiency for thermoelectric applications.