P-type Alloys Research Articles

Tuning conduction properties and clarifying thermoelectric performance of P-type half-heusler alloys TiNi1−xCoxSn (0 ≤ x ≤ 0.15)

TiNiSn is an N-type thermoelectric material with a high-power factor composed of low toxicity and abundant elements. TiNiSn also shows P-type electrical conduction by hole doping. In this study, we tune the conduction properties of TiNi1−xCoxSn (0 ≤ x ≤ 0.15) with Co substitution at the Ni site. The samples were prepared by the arc melting method, and thermoelectric properties were investigated up to 800 K. The results of the Hall effect and the Seebeck coefficient measurements indicate that the majority of charge carriers changes from electrons to holes at x ≥ 0.03, suggesting that Co acts as an acceptor. We report for the first time that Ti0.994Ni1.00Co0.051Sn1.01 exhibits ZT = 0.12 at 675 K. This work reveals that Ti0.994Ni1.00Co0.051Sn1.01 could be a potential P-type thermoelectric material operating at high temperatures.

Enhancement of thermoelectric properties in p-type ZnSb alloys through Cu-doping

To meet the growing demand for thermoelectric devices operating in intermediate temperature ranges, it is essential to develop high-performance materials with superior thermoelectric properties and robust mechanical strength. In this study, we systematically optimized carrier concentration by introducing acceptor impurities into ZnSb materials. Our results demonstrate that doping Cu into the Zn site effectively modulates hole carrier concentration, leading to a substantial enhancement in electrical conductivity and a remarkable improvement in power factor (107 %). Consequently, we achieved a high peak ZT of 1.04 at 600 K and an average ZTave value of 0.63 within the temperature range of 300–600 K. This yielded a calculated efficiency of ηmax = 7 % at ΔT = 300 K, for the Zn0.99Cu0.01Sb sample, which is 134 % higher than that of the pristine ZnSb sample (ηmax = 2.98 %). Moreover, the superior hardness and fracture toughness (KIC) of ZnSb samples compared to other state-of-the-art thermoelectric materials make them highly desirable for real-time applications.

Predicting the thermoelectric figure of merit in p-type BiSbTe-based alloys using artificial neural network modeling

The polycrystalline Bi0.5Sb1.5Te3 compound has drawn promising thermoelectric material over the decades with a figure of merit (zT) close to unity and numerous experiments have been conducted through a trial-and-error approach to further improve their zT by tuning the chemical composition and processing approaches. Despite a lot of studies available on BiSbTe alloys, choosing the right combination of alloy system with high zT is still a challenging task. Herein, we produced a p-type Bi0.5Sb1.5Te3 alloy through casting followed by high-energy milling to enhance the zT via reducing thermal conductivity. The experimental results revealed that a peak zT of 0.95 was achieved at 300 K due to a substantial reduction in thermal conductivity via enhanced carrier/phonon scattering at refined grain boundaries. In addition to the current scenario, the machine learning (ML) assisted artificial neural network (ANN) modeling was performed to predict the zT value by applying the composition, electrical conductivity, Seebeck coefficient, thermal conductivity, and temperature as the input parameters. The predicted zT by ANN modeling shows excellent accuracy with experimental findings about an average absolute error of 9.34 %. Therefore, the developed ANN modeling shows a protocol for composition-based prediction of zT with reduced experimental costs, time consumption, and excellent accuracy in terms of the theoretical and experimental databases.

Suppressed bipolar effect and high average ZTave in CuO-doped Bi0.46Sb1.54Te3 bulks with a large size

Currently, bismuth telluride-based zone-melted ingots dominate the commercial thermoelectric (TE) market. However, bismuth telluride-based zone-melted ingots with a layered lattice structure are brittle, posing challenges for their application in miniature devices. Their polycrystalline alloys have robust mechanical strength. However, the electrical conductivity of a p-type polycrystalline BiSbTe alloy bulk deteriorates. In the current study, the Bi0.46Sb1.54Te3 powder was from crushed zone-melted ingots. Large-sized polycrystalline (CuO)xBi0.46Sb1.54Te3 (x = 0, 0.003, 0.01, 0.03 and 0.1) bulks were prepared via the hot-pressing method under 65 MPa at 510°C for 15 min. The electrical conductivity was improved remarkably by the acceptor doping effect. The bipolar effect of the Seebeck coefficient and thermal conductivity at high temperatures was suppressed significantly due to increased majority carrier centration and enlarged bandgaps. Consequently, their TE performance (the dimensionless TE figure of merit, ZT) was significantly improved and the ZTmax and ZTave reached 1.4 and 1.27, respectively.

Highly effective solid solution towards high thermoelectric and mechanical performance in Bi–Sb–Te alloys via Trojan doping

We present a novel approach named Trojan doping, which utilizes NaBiS2 to increase the solubility of Na in p-type BST alloys. The ZT value and the hardness of the doped sample are 58% and 45% higher than those of the pristine sample, respectively.

Enhancement of the thermoelectric performance of half-metallic full-Heusler Mn2VAl alloys via antisite defect engineering and Si partial substitution

A half-metallic full-Heusler Mn2VAl alloy is a potential p-type thermoelectric material that can directly generate electricity from waste heat via the Seebeck effect. For practical use, the Seebeck coefficient S of Mn2VAl should be increased while maintaining a high electrical conductivity σ from its half-metallic character. Herein, we achieved this objective through antisite defect engineering. Theoretically, it was predicted that the S was maximized by regulating partial density of states of majority-spin sp-electrons through the control of the fraction of antisite defect, fAD, between V and Al atoms in Mn2VAl. Experimentally, a significant increase in S and a slight decrease in σ were observed for an Mn2VAl sample with an optimal fAD = 33%, enhancing the thermoelectric power factor PF by 2.7 times from an Mn2VAl sample with fAD = 14%. Furthermore, we combined the antisite defect engineering with a partial substitution method. An Mn2V(Al0.96Si0.04) sample with fAD = 33% exhibited the highest PF = 4.5 × 10−4 W·m−1·K−2 at 767 K among the samples. The maximum dimensionless figure-of-merit zT of the Mn2V(Al0.96Si0.04) sample with fAD = 33% was measured to be 3.4 × 10−2 at 767 K, which is the highest among the p-type half-metallic full-Heusler alloys.

Improved Thermoelectric Performance of Sb2Te3 Nanosheets by Coating Pt Particles in Wide Medium-Temperature Zone.

The p-type Sb2Te3 alloy, a binary compound belonging to the V2VI3-based materials, has been widely used as a commercial material in the room-temperature zone. However, its low thermoelectric performance hinders its application in the low-medium temperature range. In this study, we prepared Sb2Te3 nanosheets coated with nanometer-sized Pt particles using a combination of solvothermal and photo-reduction methods. Our findings demonstrate that despite the adverse effects on certain properties, the addition of Pt particles to Sb2Te3 significantly improves the thermoelectric properties, primarily due to the enhanced electronic conductivity. The optimal ZT value reached 1.67 at 573 K for Sb2Te3 coated with 0.2 wt% Pt particles, and it remained above 1.0 within the temperature range of 333-573 K. These values represent a 47% and 49% increase, respectively, compared to the pure Sb2Te3 matrix. This enhancement in thermoelectric performance can be attributed to the presence of Pt metal particles, which effectively enhance carrier and phonon transport properties. Additionally, we conducted a Density Functional Theory (DFT) study to gain further insights into the underlying mechanisms. The results revealed that Sb2Te3 doped with Pt exhibited a doping level in the band structure, and a sharp rise in the Density of States (DOS) was observed. This sharp rise can be attributed to the presence of Pt atoms, which lead to enhanced electronic conductivity. In conclusion, our findings demonstrate that the incorporation of nanometer-sized Pt particles effectively improves the carrier and phonon transport properties of the Sb2Te3 alloy. This makes it a promising candidate for medium-temperature thermoelectric applications, as evidenced by the significant enhancement in thermoelectric performance achieved in this study.

Advancement of thermoelectric performances through the dispersion of expanded graphene on p-type BiSbTe alloys

ABSTRACT We demonstrated the systematic investigation of the graphene addition on the microstructural behaviour and concurrent thermoelectric properties of water-atomized p-type BiSbTe (BST)- based alloy using mechanical ball milling, and followed through the spark plasma sintering to fabricate a bulk compact specimen. X-ray diffraction results confirm the single phase of BST. The fracture surface of both specimen exhibits the homogenous distribution of grains with irregular shapes in a random alignment. The graphene in the BST provides an extra carrier transport leading to an increment in the carrier concentration (n) resulting in higher electrical conductivity (σ) for the BST + Graphene composite. The interface between two-dimensional (2D) graphene and bulk BST provides a larger degree of phonon scattering leading to a maximum reduced thermal conductivity (к) of 0.8 W m−1K−1 compared to pristine- BST (0.9 W m−1K−1) results in a maximum figure of merit (ZT) 1.1 at 400 K.

Maximizing the scattering of multiwavelength phonons in novel biphasic high-entropy ZrCoSb-based half-Heusler alloys

The thermoelectric (TE) performance of p-type ZrCoSb-based half-Heusler (HH) alloys has been improved tremendously in recent years; however, it remains challenging to find suitable n-type ZrCoSb-based HH alloys due to their high lattice thermal conductivity (κL). In this work, n-type Zr1−xTaxCo1−xNixSb HH alloys were firstly designed by multisite alloying. The evolution of the Raman peak proved that alloy scattering, phonon softening, anharmonicity, entropy-driven disorder, and precipitates had a combined effect on decreasing κL by 46.7% compared to that of pristine ZrCoSb. Subsequently, Hf0.75Zr0.25NiSn0.99Sb0.01 was introduced into Zr0.88Ta0.12Co0.88Ni0.12Sb to further suppress κL. Remarkably, the grain size of the biphasic HH alloys was refined by at least one order of magnitude. A biphasic high-entropy HH alloy with y = 0.2 exhibited the minimum κL of ∼2.44 W/(m·K) at 923 K, reducing by 67.7% compared to that of ZrCoSb. Consequently, (Zr0.88Ta0.12Co0.88Ni0.12Sb)0.9(Hf0.75Zr0.25NiSn0.99Sb0.01)0.1 exhibited the highest TE figure of merit (∼0.38) at 923 K. The cooperation between the entropy and biphasic microstructure resulted in multiscale defects, refined grains, and biphasic interfaces, which maximized the scattering of the multiwavelength phonons in HH alloys. This work provides a new strategy for further reducing the grain size and κL of medium- and high-entropy HH alloys.

High-efficiency and reliable same-parent thermoelectric modules using Mg3Sb2-based compounds.

Thermoelectric modules can convert waste heat directly into useful electricity, providing a clean and sustainable way to use fossil energy more efficiently. Mg3Sb2-based alloys have recently attracted considerable interest from the thermoelectric community due to their nontoxic nature, abundance of constituent elements and excellent mechanical and thermoelectric properties. However, robust modules based on Mg3Sb2 have progressed less rapidly. Here, we develop multiple-pair thermoelectric modules consisting of both n-type and p-type Mg3Sb2-based alloys. Thermoelectric legs based on the same parent fit into each other in terms of thermomechanical properties, facilitating module fabrication and ensuring low thermal stress. By adopting a suitable diffusion barrier layer and developing a new joining technique, an integrated all-Mg3Sb2-based module demonstrates a high efficiency of 7.5% at a temperature difference of 380K, exceeding the state-of-the-art same-parent thermoelectric modules. Moreover, the efficiency remains stable during 150 thermal cycling shocks (∼225h), demonstrating excellent module reliability.

Coupling of electronic transport and defect engineering substantially enhances the thermoelectric performance of p-type TiCoSb HH alloy

Further advancements in thermoelectric technology rely on the capacity to control both electrical and thermal transport properties simultaneously. Although TiCoSb-based half-Heusler compounds are promising for mid-range-temperature thermoelectric applications owing to their high Seebeck coefficient and good electrical conductivity, their high thermal conductivity has been so far the main issue to overcome. Here, we show that a combined approach of tuning the electronic properties and defect engineering enhances the thermoelectric performance of p-type TiCoSb-based compounds. By alloying on the Co and Ti sites with Fe and Zr, respectively, an overall increase in the peak ZT value of up to ∼90% at 823 K is achieved in Ti0.8Zr0.2Co0.85Fe0.15Sb. This enhancement is directly tied to the more pronounced metallic nature of transport upon Fe alloying combined with a significant reduction in thermal conductivity due to mass and strain field fluctuations driven by the substitution of Zr for Ti, as evidenced by the Debye-Callaway model. Further adjusting the hole concentration with aliovalent Sn doping leads to an additional increase in ZT, eventually leading to a peak value of ∼0.54 at 823 K in Ti0.8Zr0.2Co0.85Fe0.15Sb0.96Sn0.04, which is 224% higher than in TiCo0.85Fe0.15Sb, and the highest value reported so far in Hf-free p-type TiCoSb based HH alloys.

Effect of cold and hot compactions on corrosion behavior of p- and n-type bismuth telluride-based alloys developed through microwave sintering process

Bismuth Telluride (BiTe) based p-type and n-type alloys exhibit superior thermoelectric (TE) performance covering energy requirements for specialized and home utilization. The main challenge nowadays is the sustainability of their adequate TE performance in corrosive environments, which might activate the corrosion reactions, leading to the degradation of p/n semiconductors, and then failure of the TE device. This study investigates the electrochemical responses of cold and hot compacted, microwave-sintered p- and n-type BiTe alloys in a saline medium (3.5 wt% NaCl solution). XRD analysis of microwave-sintered cold- and hot-compacted BiTe pellets confirmed their phase purity and uniform crystal structure. Potentiodynamic polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) data showed enhancements in the corrosion behavior of hot-compacted p-type and cold-compacted n-type BiTe pellets. The study also proposes a corrosion resistance mechanism with an equivalent electrical circuit (EEC) to fit the experimental EIS data of both BiTe pellets. FE-SEM analysis showed visible microstructural evolutions of the BiTe pellets and their passive films. It revealed a remarkable improvement in the microstructure and blocking effect caused by the formed passive films coating the surfaces of the pellets and acting as a physical barrier preventing the passing of destructive Cl- ions. EDX spectra have proved the presence of p-type and n-type BiTe alloys, each with the corresponding dopant element of Antimony (Sb) or Selenium (Se), respectively, and in the same weight compositions for either hot or cold compacted pellets. AFM analysis examined the surface topography of developed pellets. It showed an increment in the surface roughness-mean-square (RMS) values with the development of passive films on p- and n-type BiTe alloys.

Sb2Te3 based alloy with high thermoelectric and mechanical performance for low-temperature energy harvesting

Introducing nanostructures is an effective method to improve the performance of thermoelectric materials. However, the strength of the nano Sb2Te3 based materials deteriorates significantly between 573 and 673 K, which severely limits its application in energy harvesting. The motivation of this work is to develop p-type Sb2Te3-based alloys with high mechanical property and high figure-of-merit ZT over a wide temperature range. Fine grains and nano-twins are formed simultaneously by reducing Te content and high-energy ball milling, resulting in a lower lattice thermal conductivity and better mechanical properties. Copper doping is applied to further optimize the carrier and phonon transport behavior while maintaining excellent mechanical properties. In consequence, the ZT value of Sb1.82In0.15Cu0.03Te2.98 sample is enhanced up to 1.06 at 623 K and a fairly high ZTave of 0.76 from 300 K to 673 K is achieved. To achieve a high conversion efficiency within a wider temperature range, a p-type segment leg composed of the present material and the low-temperature Bi0.4Sb1.6Te3.01 is fabricated via one-step sintering, and it shows an efficiency as high as 9.2 % under the temperature difference of 380 K.

Augmented thermoelectric performance of LiCaX (X = As, Sb) Half Heusler compounds via carrier concentration optimization

The present study is focussed on the detailed physical insight into the structural, thermal, and dynamical properties of 8-valence electron Half Heusler (HH) compounds LiCaX (X = As, Sb) using Density functional theory. The thermal and dynamic stabilities of the compounds are assessed via ab-initio molecular dynamic simulations and phonon dispersion calculations, respectively. The Tran-Blaha modified Becke Johnson potential is used to accurately predict the band gap of investigated compounds. It is found that they are indirect band gap semiconductors with band gaps of 2.52 eV (LiCaAs) and 2.09 eV (LiCaSb). The transport parameters are obtained for p-type and n-type doping at temperatures ranging from 300 K to 800 K by solving the Boltzmann Transport equation. The deformation potential theory is employed to calculate the temperature dependent relaxation time for both compounds. The results of the various thermoelectric parameters obtained using actual values of time-dependent relaxation time are compared with that calculated under constant relaxation time approximation. The maximum power factor is 10.95 × 1011 (4.99 × 1011) Wm−1K−2s−1 for p-type (n-type) LiCaAs and 12.53 × 1011 (5.30 × 1011) Wm−1K−2s−1 for p-type (n-type) LiCaSb at optimized carrier concentration. The obtained low lattice thermal conductivities for LiCaSb (0.66 Wm−1K−1) and LiCaAs (0.88 Wm−1K−1) are explicated it in terms of different phonon modes. The Figure of Merit at 800 K for p-type (n-type) LiCaAs is as high as 0.90 (0.73) and 0.93 (0.84) for LiCaSb at optimum carrier concentration ∼1020 cm−3 (∼1019 cm−3), which has been experimentally realized in other 8-valence electron Li-based HH compounds. The good thermoelectric performance of p-type LiCaX in comparison to n-type suggests that p-type LiCaX alloys are viable candidates for high temperature energy harvesting applications.

Synergistic effects of Mg vacancy and Ag doping on thermoelectric transport properties of p-type Mg3Sb2

The defect formation energy and the electronic structures of Ag-doped Mg3-x-yAgySb2 alloys were accurately determined by carrying out first-principles calculations. The relevant crystals were prepared by using the directional solidification method and their thermoelectric properties were thoroughly investigated. From the calculated outcomes, it was demonstrated that Mg1 sites tend to form a vacancy, while Mg2 sites are preferentially substituted by the Ag atoms. The top values of the electrical conductivity and the power factor of the Mg2.95Ag0.025Sb2 alloy were improved by 25% and 10%, respectively. The increased point defect content is beneficial for enhancing the phonon scattering. In addition, the maximum ZT value of the Mg2.95Ag0.025Sb2 alloy was 1.1 – 1.45 times higher than that of the previously reported Ag-doped crystals. In the medium temperature range, the ZT values remained above 0.5, which is also considered a significant improvement compared with other types of p-type Mg3Sb2 alloys reported in the literature.

Discovery of YbNiSb-Based Half-Heusler Alloys as Promising Thermoelectric Materials

Half-Heusler materials are promising candidates for high-temperature power generation and have relatively high lattice thermal conductivity compared to other thermoelectric material systems. In this work, we report novel p-type YbNiSb-based half-Heusler alloys with a low lattice thermal conductivity (∼3.6 W m–1 K–1 at 340 K) that resulted from their large Grüneisen parameter, low sound speed, and low Debye temperature. All YbNiSb-based alloys exhibit a high carrier mobility of 30–50 cm2 V–1 s–1 at room temperature because of their relatively small effective mass. Importantly, the structural analysis reveals that Yb-rich Yb1.3Ni0.9Sb0.8 exhibits Yb/Ni and Yb/Sb substitution, indicating a wide homogeneity region of the YbNiSb phase experimentally. The adjustable Yb and Ni contents in YbNiSb-based alloys can modify the band structure around the Fermi level and significantly affect electrical transport properties. Additionally, by doping Ta at Yb sites, the carrier concentration and lattice thermal conductivity of these alloys can be manipulated. Consequently, a peak zT value of 0.45 at 823 K was achieved for Yb0.95Ta0.05NiSb. Our work demonstrates that YbNiSb-based alloys are promising p-type thermoelectric materials and suggests the possibility of exploring novel thermoelectric alloys in rare-earth nickel pnictides via tuning their composition and crystal structure.

Optimization of mixed grain size structure for enhancement of thermoelectric figure of merit in p-type BiSbTe-based alloys

Optimization of mixed grain size structure for enhancement of thermoelectric figure of merit in p-type BiSbTe-based alloys

High solubility of Al and enhanced thermoelectric performance due to resonant states in Fe2VAlx

Recently, n-type Fe2VAl-based full-Heusler systems, exhibiting high thermoelectric power factors, have sparked new interest in this material class for thermoelectric applications. In this paper, the aluminum-rich region of the L21 phasespace in Fe–V–Al is explored by a step-by-step increase in the Al content in Fe2VAlx. We reveal a promising route to improve the thermoelectric properties of p-type Heusler alloys. First, we find an ultrahigh solubility of Al in Fe2VAlx and confirm the presence of a single Heusler phase up to x = 2 using x-ray diffraction analysis and scanning electron microscopy. Second, thermoelectric transport properties, measured in a wide temperature range from 4 to 800 K, show a substantial increase in the thermopower by over 100% and a significant decrease in the thermal conductivity by up to 80% for the Al-rich samples. Detailed analysis of the carrier-concentration-dependent thermopower as well as Hall measurements indicate the formation of a resonant state at the valence band edge as a likely origin for this enhancement. This is further corroborated by density-functional-theory calculations of the electronic density of states. Our work sets the stage for p-type full-Heusler materials with enhanced thermoelectric performance, applying the principle of resonant states to this material class.

Synergistically improving the thermoelectric and mechanical performance for p-type MnGe1-xSbxTe2 alloys.

The MnGeTe2 compound crystallizes in a cubic structure without any phase transition and has great potential for enhancing the thermoelectric merit of MnGeTe2-based materials. In this work, Sb was used as an effective dopant to replace Ge sites in MnGeTe2 compounds. By optimizing the carrier concentration, excellent power factors can be obtained in the tested temperature range. Meanwhile, the characterization results show that Sb doping introduces point defects and induces grain refinement, which enhances phonon scattering and improves thermoelectric transport performance by reducing lattice thermal conductivity. Eventually, the ZT value increases from ∼0.65 for pure phase MnGeTe2 to ∼0.84 for MnGe0.90Sb0.1Te2 at 717 K by synergistic regulation of the electrical and thermal conductivities. In addition, the hardness test results of the samples show that the doping of Sb endows the MnGeTe2-based thermoelectric material with a higher Vickers hardness (>200 HV) and shows favorable mechanical properties.

Optical phonon mode assisted thermal conductivity in p-type ZrIrSb half-Heusler alloy: a combined experimental and computational study

Half-Heusler (HH) alloys with an 18 valence electron count have attracted significant interest in the area of research related to thermoelectrics (TEs). Understanding the novel transport properties exhibited by these systems with semiconducting ground state is an important focus area in this field. The large thermal conductivity shown by most of the HH alloys poses a major hurdle to improving the figure of merit (ZT). In addition, understanding the mechanism of thermal conduction in heavy-constituent HH alloys is an interesting aspect. Here, we have investigated the high-temperature TE properties of ZrIrSb through experimental studies, phonon dispersion and electronic band structure calculations. ZrIrSb is found to exhibit a substantially lower magnitude of resistivity and Seebeck coefficient near room temperature due to the existence of anti-site disorder between Ir/Sb and vacant sites. Interestingly, in ZrIrSb, lattice thermal conductivity is governed by a coupling between the acoustic and low-frequency optical phonon modes, which originates due to heavier Ir/Sb atoms. This coupling leads to an enhancement in the Umklapp processes due to the optical phonon excitations near the zone boundary, resulting in a lower magnitude of κ L. Our studies point to the fact that the simultaneous existence of two heavy mass elements within a simple unit cell can substantially decrease the lattice degrees of freedom.