SnTe Phase Research Articles

Dual-phase competitive behavior in N-type Sn–Bi–Te thermoelectric films achieving high thermoelectric performance

The dual-phase competitive behavior is introduced as an effective strategy to optimize the physical and chemical properties of N-type Bi2Te3 thermoelectric (TE) materials. Controllable SnTe-embedded Bi2Te3 nanocomposites can be synthesized with the addition of excessive Sn into Bi2Te3 by tuning the crystallization behavior under proper thermal heating temperature. Notably, the precipitation temperature of Bi2Te3 increases from 473 ​K for Sn20.9(Bi2Te3)79.1 to 573 ​K for Sn34.4(Bi2Te3)65.6, expanding the controllable temperature span for the presence of SnTe phase. The second-phase nanoprecipitate SnTe can improve electrical conductivity by competing with the Bi2Te3 phase, achieving an increase of four orders of magnitude at the critical temperature of ∼500 ​K. Simultaneously, it increases the interfacial energy filtration effect between nanocrystalline grains, decoupling electrical parameters between conductivity and Seebeck coefficient. Consequently, the high power factor of ∼147 ​μW/mK2 at 650 ​K for optimized Sn26.6(Bi2Te3)73.4 films can be obtained, which is more than twice that of the pure Bi2Te3 material. Our work demonstrates a new physical mechanism to unravel the complicated structure-property relationship by dual-phase competitive behavior during phase transition. This study fills the gap in knowledge on the effects of the SnTe phase regarding the Bi2Te3 system and provides guidance for the innovative design of high-performing inorganic thermoelectrics.

Interfacial Reactions between Sn-Based Solders and n-Type Bi2(Te,Se)3 Thermoelectric Material.

This study investigated the interfacial reactions between n-type Bi2(Te,Se)3 thermoelectric material, characterized by a highly-oriented (110) plane, and pure Sn and Sn-3.0Ag-0.5Cu (wt.%) solders, respectively. At 250 °C, the liquid-state Sn/Bi2(Te,Se)3 reactions resulted in the formation of both SnTe and BiTe phases, with Bi-rich particles dispersed within the SnTe phase. The growth of the SnTe phase exhibited diffusion-controlled parabolic behavior over time. In contrast, the growth rate was considerably slower compared to that observed with p-type (Bi,Sb)2Te3. Solid-state Sn/Bi2(Te,Se)3 reactions conducted between 160 °C and 200 °C exhibited similar interfacial microstructures. The SnTe phase remained the primary reaction product, embedded with tiny Bi-rich particles, revealing a diffusion-controlled growth. However, the BiTe layer had no significant growth. Further investigation into growth kinetics of intermetallic compounds and microstructural evolution was conducted to elucidate the reaction mechanism. The slower growth rates in Bi2(Te,Se)3, compared to the reactions with (Bi,Sb)2Te3, could be attributed to the strong suppression effect of Se on SnTe growth. Additionally, the interfacial reactions of Bi2(Te,Se)3 with Sn-3.0Ag-0.5Cu were also examined, showing similar growth behavior to those observed with Sn solder. Notably, compared with Ag, Cu tends to diffuse towards the interfacial reaction phases, resulting in a high Cu solubility within the SnTe phase.

Unveiling the optoelectronic characteristics of SnTe thin films: An extensive investigation via structural & photoresponse analysis of drop-cast deposition

Thin film on a glass slide substrate of tin telluride (SnTe) is deposited at room temperature by drop casting method. The thin films are thoroughly characterized. The study by diffraction of X-ray and Raman stated the crystalline structure and SnTe phase of the films. The films have a cubic structure with space group of Fm-3m. The Raman spectrum showed A1 and ETO vibration modes corresponding to SnTe. The microstructure study is done by optical and scanning electron microscopy. The atomic force microscopy stated the thin film to be flat having uniform even spread. The transmission electron microscopy at high-resolution supported the crystalline nature of the thin films. The spacing of fringes matched the SnTe primary crystallographic (200) plane spacing. The photoresponse of the SnTe thin film is investigated at three intensities keeping +50 mV biasing voltage. The photoresponse analysis showed the drop-casting deposited SnTe thin film offers potential for future applications.

Tin tellurium colloidal synthesis and spray pyrolysis thin films deposition: the ammonium hydroxide influence

In this research a colloidal alternative route to synthesize and the influence of ammonium hydroxide into the and phase formation at atmospheric conditions is reported. The obtained solutions at different ammonium concentration were analyzed through x-ray Diffraction to determine the structure and the phase. Meanwhile, Raman spectroscopy was used to analyze and discuss the presence of possible byproducts, those results were complemented by EDX analysis, as well as the morphology was analyzed by HRSEM. Albeit the resultant SnTe colloids were deposited as thin films by spray pyrolysis at 300 °C, following two deposit variations, the first one was one step deposition (continuous) and the second as an intermittent (I) where several layers were deposited. The resultant thin films were analyzed through HRSEM, XRD and profilometry correlating the morphology, and structural properties to those obtained from the colloids.

Microstructural and thermal evaluation of the formation of tin–tellurium (Sn[sbnd]Te) alloy by ball milling process

A mechanically induced phase transition in tin‑tellurium (SnTe) system and its dependence on the milling time of the masses of metastable SnTe phase(s) produced during ball milling have been investigated. The synthesis approach involves top-down ball milling of elemental Sn and Te powders in an argon environment with a milling time of 1 to 5 h at a low ball milling speed of 300 RPM. The SnTe solid solution forms as particles, resulting in large masses due to the ball milling operation. Ball milling of initial micron-sized powders of Sn and Te resulted in a homogenized nano-sized powder mixture. This mechanical mixture of Sn and Te powders exhibiting intermediate phases with a crystal structure similar to that of elemental Sn and Te were detected in the ball-milled mixtures at various milling times, which resulted in a stable phase that ultimately transformed into a SnTe solid solution. Morphological and structural modifications at different stages of ball milling were investigated through X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry, dynamic light scattering, density measurement, and surface analysis. Subsequently, dense pellets were fabricated by spark plasma sintering from synthesized SnTe solid-solution powders produced by ball milling for 5 h. The sintered samples showed excellent structural integrity with densities of up to 6.35 g/cm3. It is to be noted that the formation of large quantities of uniform SnTe powder alloy produced by ball milling is reported for the first time in this study. These findings could be extended in the future to prepare bulk quantities of many solid solutions of the elements of the same periodic group.

Mechanistic insights into antibacterial and anti-biofilm activities against multidrug-resistant microbes of SnTe nanospheres synthesized by sonochemical method

The sonochemical method is used to synthesize SnTe nanoparticles (Nps). Elemental analyses validated the stoichiometry of the nanoparticles. The phase and structure of the unit cell are verified by X-ray diffraction which shows nanoparticles are SnTe phase and a cubic crystal structure with a unit-cell lattice parameter of 6.31 Å having Fm-3m space group (No. 225), with Z = 4. The spherical form of nanoparticles is confirmed by electron microscopy. The Raman investigation showed a distinctive peak at 128.10 cm−1 connected to SnTe. The HR-TEM scans demonstrate that the Nps has size ranging between 25 and 30 nm and SnTe phase is confirmed by match of fringe pattern d-spacing. The SnTe Nps showed antibacterial properties through the formation of biofilms. The as-synthesized nanoparticles showed an efficient anti-microbial effect on staphylococcus aureus (MTCC 9542), listeria monocytogenes (MTCC 657), and proteus vulgaris (MTCC 426) bacteria. The study showed 100% growth suppression after 24 h of treatment with SnTe Nps, demonstrating the antimicrobial efficacy of SnTe Nps. The MIC (IC50) of 20 μg/mL for staphylococcus aureus is found to be resistant to the SnTe Nps effective anti-biofilm action. Based on these results, the authors looked into the feasibility of coating surfaces with the sample to prevent the growth of biofilms.

Thermal analysis and non-isothermal crystallization kinetics of Ag–Ga2Te3–SnTe telluride glasses

In this paper, the microstructure evolutions and crystallization kinetics of the newly developed Agx-[(Ga2Te3)34(SnTe)66]100−x (x = 6, 8 and 10%) telluride glasses were comprehensively investigated under non-isothermal conditions. The microscopic structure of the investigated samples were analyzed by X-ray diffraction (XRD), transmission electron microscope (TEM) and the selected area electron diffraction (SAED). The crystalline products were identified as the SnTe phase (primary crystalline phase) and Ga6SnTe10 phase. The exothermic crystallization process for any investigated samples was actually on the envelope of two overlapped peaks and could be assigned to the first crystallization event of SnTe precipitation and followed by the second crystallization event of Ga6SnTe10 phase. The crystallization mechanism and activation energies were estimated by Matusita–Sakka model under continuous heating based on the differential scanning calorimeter (DSC). For the first crystallization event, the Avrami exponent n values for each of the three investigated samples was approximately 3, suggesting the crystallization occurred through the two-dimensional growth with increasing number of nucleation. The values of n for the second crystallization event of Ga6SnTe10 phase were close to 4, indicating three-dimensional growth with a increasing number of nuclei. The activation energy Ec for both the first and second crystallization events was gradually decreased as the Ag content increased.

A Comprehensive Study of Sn-Ga2Te3-SnTe Amorphous Alloys: Glass Formation and Crystallization Kinetics

In this paper, newly developed tellurium-based [(Ga2Te3)34(SnTe)66]100-x-Snx amorphous alloys were prepared by the melt-spun method, with a linear velocity of 40 m/s and injection pressure of 20 kPa under an Ar atmosphere. The glass-forming region was identified in the range of x = 0 to 10 mol%. The glass transition temperature Tg and crystallization onset temperature Tc decreased monotonically with the increasing Sn content in the whole compositional range, resulting in the decrease in the stability criterion ΔT from 33 K (S2) to 23 K (S10). The crystallization kinetics were systematically investigated based on the differential scanning calorimeter (DSC) under non-isothermal conditions. The activation energies of the S8 amorphous sample determined by Kissinger and Ozawa equations were Eg (201.1~209.6 kJ/mol), Ec (188.7~198.3 kJ/mol), Ep1 (229.8~240.1 kJ/mol) and Ep2 (264.2~272.6 kJ/mol), respectively. The microscopic structure of the S8 amorphous sample and its annealed glass-ceramics were also analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). The crystalline products were identified as having a SnTe phase (primary crystalline phase) and Ga6SnTe10 phase, thus providing a promising candidate for the development of high-performance thermoelectric glass-ceramic materials.

Kinetic stability of tin telluride nanoparticles synthesized by hydrothermal method

Nanoparticles of tin telluride (SnTe) are prepared by the hydrothermal method. The analysis of composition showed the nanoparticles to be stoichiometric. The structure and phase are determined by X-ray diffraction. It showed the nanoparticles possess cubic structure and SnTe phase. The spherical shape of the nanoparticles is validated by electron microscopy. The Raman spectrum revealed the characteristic peak associated with SnTe. The thermal analysis study of SnTe nanoparticles are done to comprehend the thermal nature. The study is done in inert nitrogen for heating rates of 5, 10, 15 and 20 K•min−1 in the range of temperature between ambient and 1053 K. The nanoparticles decompose by three steps. Isoconversional model free methods of Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa and Friedman are employed to determine the thermodynamic parameters. The results are investigated in details.

Simultaneous Seebeck coefficient and electrical conductivity enhancement of GeSbTe films via Sn addition

Sn-added GeSbTe (GST) thin films were deposited using a co-magnetron sputtering technique. The effects of varying the Sn content through a variable Sn target sputtering power and post annealing at 673 K were investigated. The DC power density applied to the GST target was controlled at 50 W, while the power density of the Sn target was increased from 0 W to 40 W. The results demonstrate the coexistence of the fcc-GST, hcp-GST and SnTe phases in the Sn-added GST thin films. The substitution of Sn at the Ge-site increases the crystallization speed and leads to defects and lattice disordered local arrangement in the GST films, causing the Seebeck coefficient to increase. The SnTe phase was created as a result of the high Sn content in the sample due to the over-doping limit of Sn into the GST structure. The presence of SnTe in Sn-doped GST films increased the electrical conductivity. The maximum power factor of 17.0 μW/cmK2 at 450 K was obtained at an Sn content of 14.7 at%. These results indicated that the thermoelectric properties of Sn-doped GST films were improved via the formation of an appropriate amount of SnTe composite.

Nanostructured Te‒SnTe eutectic composites with enhanced thermoelectric performance

The eutectic Te‒SnTe composites were successfully prepared via a melt spinning method combined with a spark plasma sintering technique. The differences in thermoelectric properties for alloys near the eutectic composition were investigated. These composites could benefit from both the higher electrical conductivity of the SnTe phase and the superior Seebeck coefficient of the Te phase. The eutectic Sn-90at%Te composite exhibits an enhanced thermoelectric performance. Its maximum ZT is 1.8–2.1 times higher than that of pristine SnTe and Te materials. Upon doping with the Sb element, the electrical transport behavior could be further improved. Large amounts of grain boundaries and phase interfaces can readily scatter phonons. Combined with the extra scattering from nanoprecipitates, dislocations, and strain fields, an ultralow lattice thermal conductivity of 0.49 W m−1 K−1 could be obtained for the Sn-90at%Te-2.0at%Sb alloy at 633 K. The improved thermoelectric properties for the Te‒SnTe eutectic system provide a new strategy to explore high-performance materials.

Exotic colony formation in Sn-Te eutectic system

Eutectics are self-organized composite materials that exhibit a wide variety of microstructural features. Besides intrinsic materials properties like interfacial energies or diffusivities as well as the nature of the phase diagrams, the process parameters such as magnitude and orientation of the temperature gradient as well as the velocity of the growth interface influence the evolution of the microstructure. Recently, we have observed the evolution of complex patterns due to addition of ternary impurities in the binary Sn-Te system that contains, in addition to (Te), an intermetallic SnTe phase with a cubic crystal structure. This paper examines in detail the origin of such a microstructure that arises due to a two-phase growth instability induced by impurity addition. The binary eutectics (Sn-Te) and ternary eutectics (Sn-Te with an impurity addition) are directionally solidified at different interfacial velocities in order to study the morphological evolution. The binary alloy exhibits a rod-like or an interconnected string of rods morphology while the addition of a third component leads to a diffusive instability (similar to a Mullins-Sekerka instability) that results in the formation of two-phase colonies. The onset of instability depends on both the growth velocity and impurity concentration while the growth direction of the cells is normal to the {0001} planes of (Te) and {111} planes of SnTe. Through the extensive use of multiple characterization techniques, we have explored the morphological characteristics and crystallography of these colonies. The colonies have a complex internal structure that bears a three-fold symmetry reminiscent of the trigonal symmetry of the (Te) crystal, arising possibly because of strong anisotropy in the solid-liquid interfacial energy or in the kinetics of growth. For the different impurity additions (Ag or Sb), the internal eutectic morphology of the colony, due to the addition of Ag is different from that observed for the addition of Sb. The latter leads to the formation of lamellae while a rod-like feature could be observed for impurities like Ag. The complex patterns exhibit a structural hierarchy that provides opportunities for designing novel materials.

Effects of the Ni electrodeposit on microstructure evolution and electrical resistance of the P-type Bi2Te3 solder joint

Abstract A systematic investigation was carried out to evaluate the effect of Ni electrodeposit on the microstructure evolution and electrical resistance of the P-type Bi2Te3-based thermoelectric (TE) joint. In this study, two systems (SAC305/(Bi,Sb)2Te3 and SAC305/Ni/(Bi,Sb)2Te3) were set up. The intermetallic compounds (IMCs) were mainly detected by using scanning electron microscope (SEM), X-ray diffractometer (XRD) and transmission electron microscope (TEM). A model of overlapping joint was set up for electrical resistance testing. Results indicated that the SnTe phase was the major and thermodynamically stable product in the SAC305/(Bi,Sb)2Te3 system, and its porous structure determined the presence of micro-tunnels, which facilitated the diffusion process of Sn and Te atoms, therefore the SnTe layer continuously grew in the whole reflowing duration. In this system, the time exponent was analyzed to be 1.2741, indicating that the growth of the IMC layer followed the linear law, and was reaction-controlled. In the SAC305/Ni/(Bi,Sb)2Te3 system, it was remarkable that the Ni barrier inhibited the rapid growth of the IMC layer, and the dominated product was detected to be (Ni,Cu)3Sn4 whose dense distribution could effectively suppress the diffusion of Sn atoms. The time exponent in this system was 0.5010, indicating that the growth of the Ni–Cu–Sn ternary IMC followed the parabolic laws and was mainly volume diffusion-controlled. After reflowing treatment, the electrical resistance remained at 2.203 mΩ for NiTL (the TE leg with the Ni electrodeposit) system while that of TL (the TE leg without the Ni electrodeposit) system rapidly increased to a higher value about 4.879 mΩ. Owing to the lower growth rate of the IMC layer in NiTL system, it could reasonably conclude that the Ni electrodeposit was of great importance in depressing the electrical resistance.

Electrochemical Atomic Layer Epitaxy Deposition of Ultrathin SnTe Films

Tin telluride (SnTe) ultrathin films were deposited electrochemically on polycrystalline and monocrystalline gold substrates using the electrochemical atomic layer epitaxy (ECALE) method. The electrochemical behaviors of Sn and Te were studied systematically by means of cyclic voltammetry. Cyclic voltammetry curves for Sn displayed a broad peak in the region between -0.15 V and -0.35 V, which was related to the under-potential deposition (UPD), while the curves for Te displayed a peak at 0.3 V for Te UPD. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) were employed for the characterization of the ultrathin SnTe films. XRD and Raman spectroscopy confirmed the deposition of a single SnTe phase, while SEM revealed that the deposits were composed of nanocrystallites.

Microstructure and enhanced thermoelectric performance of Te–SnTe eutectic composites with self-assembled rod and lamellar morphology

The eutectic Te–SnTe composites with self-organized rod and lamellar structure were synthesized using the directional solidification technology. The experiments show that the volume fraction and shape-tunable morphology of the SnTe phase vary with the alloy compositions. The thermoelectric properties of the composites are dependent on the volume fraction of SnTe phase and exhibit obvious anisotropy in different growth directions. The composites perpendicular to the growth direction possess much larger S and lower κL than that in the parallel direction. High resolution transmission electron microscopy (HRTEM) results illustrate that there are a given amount of dislocations and atomic mismatch stress field around the Te–SnTe eutectic interface areas, which effectively scatter the heat-carrying phonons, leading to an ultralow lattice thermal conductivity of 0.64 Wm−1K−1 for Sn-80at%Te eutectic alloy. The obtained maximum figure of merit is 0.40 for Sn-90at%Te alloy which is 1.5–1.9 times higher than that of pure SnTe and Te, respectively. It demonstrates that introducing large amounts of eutectic interfaces in Te–SnTe composites is an effective way to enhance the thermoelectric performance.

Microstructure and crystallization kinetics of Ge2Sb2Te5–Sn phase change materials

In this paper, the effects of Sn doping on the microstructure and electrical properties of amorphous and crystalline Ge2Sb2Te5 thin films are reported. The thin films bonding states are measured through X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy, which prove that the bonding states of Ge2Sb2Te5–Sn thin films regularly change with the additions of various Sn contents. Sn atoms alter the chemical surrounding of Te atoms significantly, having a low impact on the bonding environment of Sb atoms, since the additional Sn atoms bond with Te atoms and lead to the SnTe phase formation. Both the homogeneity of bonding characteristics and crystallinity in Ge2Sb2Te5–Sn thin films are improved. The atomic arrangement of the crystalline states Ge2Sb2Te5–Sn thin films is also obtained. It could be inferred that the Sn addition lead to higher crystalline interplanar spacing and arrangement of many disordered atoms. Furthermore, the corresponding activation energy value (EA) of Ge2Sb2Te5–Sn thin films is calculated. This display that the EA values of Ge2Sb2Te5–Sn increase compared to the pure Ge2Sb2Te5 thin films, since the Ge2Sb2Te5–Sn thin film structures are stabilized due to the compressed bonds and various bonding states.

Structural, Thermal, Optical, and Photoacoustic Study of Mechanically Alloyed Nanocrystalline SnTe

A nanostructured SnTe phase was produced by mechanical alloying after 2 h of milling. Part of the as-milled powder was annealed and its X-ray diffraction (XRD) pattern was recorded. The XRD patterns of the as-milled and annealed samples were refined using the Rietveld method. After annealing, partial decomposition of the SnTe phase was observed and corroborated by estimating the mean crystallite size using a Willianson-Hall plot. The Cowley-Warren parameter αSnTeCWfor the first coordination shell was calculated, showing a preference for homopolar pairs. This preference is consistent with the partial decomposition observed. According to the optical absorbance spectra, the band gap energy is inversely proportional to crystallite size, following a decaying exponential function. From the photoacoustic absorption spectroscopy measurements, the thermal diffusivity parameter and the transport properties of as-milled and annealed SnTe powder were determined.

Cubic Crystal-Structured SnTe for Superior Li- and Na-Ion Battery Anodes.

A cubic crystal-structured Sn-based compound, SnTe, was easily synthesized using a solid-state synthetic process to produce a better rechargeable battery, and its possible application as a Sn-based high-capacity anode material for Li-ion batteries (LIBs) and Na-ion batteries (NIBs) was investigated. The electrochemically driven phase change mechanisms of the SnTe electrodes during Li and Na insertion/extraction were thoroughly examined utilizing various ex situ analytical techniques. During Li insertion, SnTe was converted to Li4.25Sn and Li2Te; meanwhile, during Na insertion, SnTe experienced a sequential topotactic transition to NaxSnTe (x ≤ 1.5) and conversion to Na3.75Sn and Na2Te, which recombined into the original SnTe phase after full Li and Na extraction. The distinctive phase change mechanisms provided remarkable electrochemical Li- and Na-ion storage performances, such as large reversible capacities with high Coulombic efficiencies and stable cyclabilities with fast C-rate characteristics, by preparing amorphous-C-decorated nanostructured SnTe-based composites. Therefore, SnTe, with its interesting phase change mechanisms, will be a promising alternative for the oncoming generation of anode materials for LIBs and NIBs.

The correlation of electrical conductivity with the microstructure of Ge2Sb2Te5 thin films alloyed with Sn

In this research, the effects of Sn alloying on structure transformation and electrical characteristics of Ge2Sb2Te5 (GST) thin films were studied. It was discovered that the SnTe phase formed in GST thin films when Sn content exceeded 26 at%, and the addition of Sn atoms expanded the lattice parameter, as a result of atomic radii difference between Ge and Sn atoms. Furthermore, temperature dependent sheet resistance measurements on the GST:Sn thin films were performed for the electrical characteristics to be studied. Sn substitution fraction of 16 at% was discovered to maximize the crystallization temperature of GST thin films. Compared to the GST thin films, crystallization temperature difference and lower amorphous resistance of the GST:Sn thin films were mainly due to lower bonding energy of Sn–Te. Moreover, the amorphous conductivity activation energies (Eσ) corresponding to different grain sizes were calculated with the Arrhenius equation. The Eσ value of GST:Sn thin films decreased significantly as the Sn content increased due to grain size effects, which appears to improve the temperature stability of conductivity of phase change memory.

Effects of current stressing on the p-Bi2Te3/Sn interfacial reactions

The Sn/p-Bi2Te3/Sn sandwich-type sample was current stressed with a density of 150 A/cm2 to investigate the effects of current stressing on the p-Bi2Te3/Sn interfacial reactions. Asymmetrical heating phenomenon was observed at the anodic Sn/p-Bi2Te3 (50 °C) and cathodic p-Bi2Te3/Sn (120 °C) interfaces due to the Peltier effect. Besides the Peltier effect, the electromigration effect also influenced the growth of the SnTe phase and therefore polarity growth behavior was observed at the two interfaces. The growth of the SnTe phase at the cathodic p-Bi2Te3/Sn interface was accelerated because Peltier and electromigration effects drove more Sn atoms (dominant diffusion species) for the phase growth. By measuring the electromigration-induced atomic flux of Sn, the product of diffusivity and effective charge number (D × z*) was calculated to be 6.3 × 10−9 cm2 s−1 at 120 °C.