Sn Te Research Articles

Phase equilibria and structural investigations of the general NiAs-type in the ternary system Ni–Sn–Te

The ternary system Ni–Sn–Te was investigated by means of light optical microscopy (LOM), powder X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectroscopy (EDX). Two isothermal sections at 600 and 800 °C were investigated experimentally. The two ternary compounds, Ni5.78SnTe2 (space group I4/mmm, Pearson symbol tI18) and Ni3−xSnTe2 (space group P63/mmc, Pearson symbol hP12), already known from literature, were confirmed, although Ni3−xSnTe2 was found only at 600 °C. At higher temperatures a continuous phase field of the general NiAs-type structure was discovered between NiTe2−x and Ni3Sn2 HT. It ranges continuously from 34 to 63 at.% Ni, covering CdI2-types, as well as Ni2In-type domains; thus a continuous transition from the CdI2 to Ni2In type is confirmed, to the best of our knowledge, for the first time. Lattice parameter variations and the transition CdI2–NiAs–Ni2In in the ternary phase field were analysed.Furthermore, vertical sections at 10, 40, 55, 60 and 70 at.% Ni were determined. A liquidus surface projection and a reaction scheme of the system were constructed as well. Altogether, 17 invariant phase reactions, including 3 eutectic reactions, 2 peritectic reactions, 11 transition reactions and one maximum were discovered.

Evidence for massive bulk Dirac fermions in Pb1−xSnxSe from Nernst and thermopower experiments

Topological surface states protected by mirror symmetry are of interest for spintronic applications. Such states were predicted to exist in the rocksalt IV-VI semiconductors, and several groups have observed the surface states in (Pb,Sn)Te, (Pb,Sn)Se and SnTe using photoemission. An underlying assumption in the theory is that the surface states arise from bulk states describable as massive Dirac states, but this assumption is untested. Here we show that the thermoelectric response of the bulk states displays features specific to the Dirac spectrum. By relating the carrier density to the peaks in the quantum oscillations, we show that the first (N=0) Landau level is non-degenerate. This finding provides robust evidence that the bulk states are indeed massive Dirac states. In the lowest Landau level, Sxx displays a striking linear increase versus magnetic field characteristic of massive Dirac fermions. In addition, the Nernst signal displays a sign anomaly in the gap-inverted phase at low temperatures.

Topological crystalline insulator (Pb,Sn)Te: Surface states and their spin polarization

Using a tight-binding approach we study theoretically the nature of surface states in Pb0.4Sn0.6Te - the newly discovered topological-crystalline-insulator. Apart from the studied before (001) surface states, two other surface families, {011} and {111}, in which the mirror symmetry of the crystal's rock-salt structure plays the same role in topological protection, are considered. Our calculations show that while in (111) surface states of (Pb,Sn)Te four single topologically protected Dirac-cones should appear, for the (110) surface states the protection is lifted for two L points. In this case, instead of the Dirac points energy gaps occur in the surface states, due to the interaction between the two L valleys. In all studied cases a chiral spin texture is obtained.

Regional patterns of changing beach morphology at a decadal scale

Bradbury AP, Cope SN, Wilkinson C and Mason TE, 2013. Regional patterns of changing beach morphology at a decadal scale In: Conley, D.C., Masselink, G., Russell, P.E. and O’Hare, T.J. (eds.), Proceedings 12 th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 452-457, ISSN 0749-0208. The Southeast Regional Coastal Monitoring Programme commenced in 2002 and is on-going. In excess of 1000 km of open coast and estuarine shoreline are monitored at high resolution with a number of tools and at a range of spatial and temporal scales. The programme provides input to flood and coastal erosion risk management at a range of scales, from region-wide shoreline management plans, to detailed and localised geomorphological assessments. Detailed baseline surveys are repeated typically once every 5 years and three full surveys exist now for the entire coast. Sampling of the baseline surveys is conducted typically at biannual temporal interval. Annual analysis is conducted summarising coastal changes within coastal sub cells at a scale of typically 10-100 km. All data from the project are currently freely available via the project website (www.channelcoast.org). Examples are used to illustrate the challenges associated with analysis of coastal geomorphological change over decadal and annual temporal scales. Differentiation between natural coastal processes and management practices are explored.

Calorimetric study of specific heat in glassy Se–Te–Sn–Bi system using MDSC technique: effect of Bi incorporation

Bismuth has historical significance as a modifier in chalcogenide glasses due to the p- to n-type transition at a particular composition of definite glassy systems after its incorporation. We have synthesized some new quaternary glasses using Bi as a modifier in ternary Se78Te20Sn2 alloy as parent glass in light of this information. Modulated differential scanning calorimetry measurements have been made on glassy Se78− x Te20Sn2Bi x (0 ≤ x ≤ 6) alloys for specific heat studies. We have observed an expected enormously large increase in the specific heat values in the glass transition region. The composition dependence of specific heat values above the glass transition temperature (Cpe ) and below the glass transition (Cpg ) is also discussed in this article.

Coherent and incoherent phase stabilities of thermoelectric rocksalt IV-VI semiconductor alloys

Nanostructures formed by phase separation improve the thermoelectric figure of merit in lead chalcogenide semiconductor alloys, with coherent nanostructures giving larger improvements than incoherent nanostructures. However, large coherency strains in these alloys drastically alter the thermodynamics of phase stability. Incoherent phase stability can be easily inferred from an equilibrium phase diagram, but coherent phase stability is more difficult to assess experimentally. Therefore, we use density functional theory calculations to investigate the coherent and incoherent phase stability of the IV--VI rocksalt semiconductor alloy systems Pb(S,Te), Pb(Te,Se), Pb(Se,S), (Pb,Sn)Te, (Sn,Ge)Te, and (Ge,Pb)Te. Here we use the term coherent to indicate that there is a common and unbroken lattice between the phases under consideration, and we use the term incoherent to indicate that the lattices of coexisting phases are unconstrained and allowed to take on equilibrium volumes. We find that the thermodynamic ground state of all of the IV--VI pseudobinary systems studied is incoherent phase separation. We also find that the coherency strain energy, previously neglected in studies of these IV--VI alloys, is lowest along $[111]$ (in contrast to most fcc metals) and is a large fraction of the thermodynamic driving force for incoherent phase separation in all systems. The driving force for coherent phase separation is significantly reduced, and we find that coherent nanostructures can only form at low temperatures where kinetics may prohibit their precipitation. Furthermore, by calculating the energies of ordered structures for these systems we find that the coherent phase stability of most IV--VI systems favors ordering over spinodal decomposition. Our results suggest that experimental reports of spinodal decomposition in the IV--VI rocksalt alloys should be re-examined.

Thermodynamic studies on Sn–Te–O system

The standard Gibbs energy of formation of tin tellurate, SnTe3O8(s) was determined from its vapour pressure measurements over the temperature range 973–1,158 K by employing thermogravimetry-based transpiration method. The temperature dependence of vapour pressure of TeO2 over the mixture SnTe3O8(s) + SnO2(s) generated by the incongruent vapourisation reaction, SnTe3O8(s) → SnO2(s) + 3 TeO2(g) could be represented as: log (p (TeO2, g)/Pa ± 0.03) = 13.943–14,181 (K/T) (973–1,158 K). The standard Gibbs energy of formation of SnTe3O8(s) was also determined by measuring the oxygen potential of SnO2(s)–Te(s)–SnTe3O8(s) phase mixture by the electromotive force method. Enthalpy increments of SnTe3O8(s) were determined by inverse drop calorimetric method in the temperature range 523–973 K. The thermodynamic functions, viz., heat capacity, entropy and free energy functions were derived from the measured values of enthalpy increments. A mean value of −1,642 ± 2.0 kJ mol−1 was obtained for \( \Updelta_{\text{f}} H_{298}^{\circ } \)(SnTe3O8, s) by combining the value of Δf \( G^{\circ } \)(SnTe3O8, s) derived from vapour pressure data and the free energy functions derived from the drop calorimetric data.

Liquidus projection and phase equilibria isothermal section of Se–Sn–Te system

Ternary Se–Sn–Te alloys have important applications in thermoelectricity, optical recording and infrared devices. Air-cooled and 250°C-equilibrated ternary Se–Sn–Te alloys were prepared in this study. The primary solidification phases were determined for the air-cooled alloys and these were used to construct the liquidus projection. The liquidus projection contains seven primary phase regions and three ternary invariant reactions. The temperatures of the invariant reaction were determined by thermal analysis as occurring at 230°C, 400°C and 420°C, respectively. Using the equilibrium phases of the thermally equilibrated ternary alloys determined in this study and the phase diagram information of the three binary constituent systems, the 250°C isothermal section of the Se–Sn–Te ternary system was constructed. The equilibrated solubility of Se in SnTe is about 4at%Se and is less than that of Te in SnSe, which is about 10at%Te. No ternary compound was found in either the liquidus projection or the isothermal section.

Determination of specific heat in multi-component chalcogenide glasses of Se–Te–Sn–Pb system using modulated differential scanning calorimetry

In the recent past, glass physicists have focused their attention on the element lead as a modifier due to observation of carrier-type reversal in chalcogenide glasses for a particular composition of certain glassy systems after the incorporation of lead. Keeping this fact in mind, some new quaternary glasses have been synthesized using Pb as modifier in the ternary Se78Te20Sn2 alloy parent glass. Specific heat studies have been made in glassy Se78−xTe20Sn2Pbx(0≤x≤6) alloys using the modulated differential scanning calorimetry (MDSC) technique. An extremely large increase in the specific heat values has been observed at the glass transition temperature. The composition dependence of specific heat values below glass transition temperature (Cpe) and after glass transition (Cpg) has been also explained.

Simultaneous measurements of thermal conductivity and thermal diffusivity of Se90−x Te5Sn5In x (x = 0, 3, 6, and 9) multi-component chalcogenide glasses

Measurements of thermal conductivity and thermal diffusivity of twin pellets of Se90−x Te5Sn5In x (x = 0, 3, 6, and 9) chalcogenide glasses were carried out at room temperature using transient plane source technique. The measured values of thermal conductivity and thermal diffusivity were used to determine the specific heat per unit volume of these glasses in the composition range of investigation. Results indicated that both values of thermal conductivity and thermal diffusivity were increased with addition of indium concentration at the cost of selenium, whereas the specific heat per unit volume was slightly decreases with increase of indium content. This compositional dependence behavior of the thermal conductivity and diffusivity can be explained in terms of the iono-covalent type of bonds, which In (indium) makes with Se as it is incorporated in the Se–Te–Sn glass.

Studies on electrical switching behavior and optical band gap of amorphous Ge–Te–Sn thin films

Amorphous thin film Ge15Te85-xSnx (1 <= x <= 5) and Ge17Te83-xSnx (1 <= x <= 4) switching devices have been deposited in sandwich geometry using a flash evaporation technique, with aluminum as the top and bottom electrodes. Electrical switching studies indicate that these films exhibit memory type electrical switching behavior. The switching fields for both the series of samples have been found to decrease with increase in Sn concentration, which confirms that the metallicity effect on switching fields/voltages, commonly seen in bulk glassy chalcogenides, is valid in amorphous chalcogenide thin films also. In addition, there is no manifestation of rigidity percolation in the composition dependence of switching fields of Ge15Te85-xSnx and Ge17Te83-xSnx amorphous thin film samples. The observed composition dependence of switching fields of amorphous Ge15Te85-xSnx and Ge17Te83-xSnx thin films has been understood on the basis of Chemically Ordered Network model. The optical band gap for these samples, calculated from the absorption spectra, has been found to exhibit a decreasing trend with increasing Sn concentration, which is consistent with the composition dependence of switching fields.

ChemInform Abstract: New Mixed Palladium—Lead and Palladium—Tin Tellurides of the NiAs Type.

AbstractNew phases of the Pd—Pb—Te and Pd—Sn—Te systems belonging to the NiAs structure type are synthesized from the elements (750 °C, 8—10 h) and characterized by powder XRD.

Thermal stability and crystallization kinetics of Se–Te–Sn alloys using differential scanning calorimetry

Abstract The present article deals with the differential scanning calorimetric (DSC) study of Se–Te glasses containing Sn. DSC runs are taken at four different heating rates (10, 15, 20 and 25 K min−1). The crystallization data are examined in terms of modified Kissinger, Matusita equations, Mahadevan method and Augis and Bennett approximation for the non-isothermal crystallization. The activation energy for crystallization (Ec) is evaluated from the data obtained at different heating rates. Activation energy of glass transition is calculated by Kissinger's relation and Moynihan theory. The glass forming tendency is also calculated for each composition. The glass transition temperature and peak crystallization temperature increases with the increase in Sn % as well as with the heating rate.

Glass transition, thermal stability and glass-forming tendency of Se 90− xTe 5Sn 5In x multi-component chalcogenide glasses

Glass transition kinetics of glassy Se 90− x Te 5Sn 5In x ( x = 0, 3, 6 and 9) alloys have been investigated using differential scanning calorimetric (DSC) technique under non-isothermal conditions at different heating rates 5, 10, 15 and 20 K/min. It is observed that in these glasses, the glass transition temperature ( T g ) is found to be dependent on composition and heating rates. The activation energy of glass transition ( E g ), fragility index ( F) and stability parameter ( S) are evaluated for glassy Se–Te–Sn–In alloys. The glass transition activation energy ( E g ) and fragility index ( F) were found to be minimum at 9 at.% of In, as well as thermal stability parameter ( S) was found to be maximum at same glassy composition due to maximum crosslinking structures. Results indicate that thermal stability increases on the addition of In to ternary Se 90Te 5Sn 5 glass. Hence Se 81Te 5Sn 5In 9 glass is the better thermally stable glass in this system.

The electrical switching and thermal behavior of bulk Ge15Te85 − xSnx and Ge17Te83 − xSnx glasses

Bulk Ge15Te85−xSnx and Ge17Te83−xSnx glasses, are found to exhibit memory type electrical switching. The switching voltages (Vt) and thermal stability of Ge15Te85−xSnx and Ge17Te83−xSnx glasses are found to decrease with Sn content. The composition dependence of Vt has been understood on the basis of the decrease in the OFF state resistance and thermal stability of these glasses with tin addition. X-ray diffraction studies reveal that no elemental Sn or Sn compounds with Te or Ge are present in thermally crystallized Ge–Te–Sn samples. This indicates that Sn atoms do not interact with the host matrix and form a phase separated network of its own, which remains in the parent glass matrix as an inclusion. Consequently, there is no enhancement of network connectivity and rigidity. The thickness dependence of switching voltages of Ge15Te85−xSnx and Ge17Te83−xSnx glasses is found to be linear, in agreement with the memory switching behavior shown by these glasses.

New mixed palladium—lead and palladium—tin tellurides of the NiAs type

New ternary mixed nickel arsenide-type palladium and platinum—Group 14 metal tellurides were searched for by the high-temperature ampoule synthesis combined with the X-ray powder diffraction analysis. As a result, new phases of the ternary Pd—Pb—Te and Pd—Sn—Te systems belonging to the NiAs structure type were synthesized. The crystal structure of the compound PdPb0.304(5)Te0.695(5) was determined by the Rietveld method (P63/mmc, a = 4.151(1) A, c = 5.680(1) A, Z = 2, R1 = 0.032, Rp = 0.075, wRall = 0.025). It was shown that no ordering exists in the occupancy of the main-group atom site by lead and tellurium. In the Pd—Sn—Te system, a phase isostructural with the above-mentioned compound was found. In the latter phase, there is also no ordering in the occupancy of the main-group atom site. According to the electron diffraction data, a superstructure derived from the NiAs type exists in a narrow range of the compositions PdSn0.3Te0.7—PdSn0.4Te0.6.

Compositional dependence of thermal stability, glass-forming ability and fragility index in some Se–Te–Sn glasses

Non-isothermal DSC thermograms were obtained for the ternary Se 90Te 10− x Sn x ( x = 2, 4, 6 and 8) chalcogenide glasses in order to determine the melting temperature T m, glass transition temperature T g, onset T c and peak T p temperatures of crystallization. These temperatures were utilized to investigate the thermal stability through the calculations of temperature difference ( T c − T g), the glass transition activation energy E t, the parameter S and the average value of crystallization rate factor 〈 K p〉. In addition, the glass forming ability was estimated by the criteria of reduced glass transition temperature, T rg and Hruby parameter H R. The fragility index m for the present glasses was determined in order to see whether these materials are obtained from strong or fragile glass-forming liquid. Results reveal that, both thermal stability and glass forming ability exhibit a maximum at x = 4 at.% of Sn. Meanwhile, the prepared glasses were obtained from strong glass-forming liquid as evident from the fragility index calculations. The compositional dependence of the above parameters was discussed on the basis of Philips and Thorpe topological model and the critical composition occurs at an average coordination number 〈 r〉 = 2.16 but not 2.40. This is due to the formation of iono-covallent bonds when the glass doped with heavy elements like Sn.

The effect of indium additive on crystallization kinetics and thermal stability of Se–Te–Sn chalcogenide glasses

The crystallization kinetics of bulk Se 90− x Te 5Sn 5In x ( x=0, 3, 6 and 9) multi-component chalcogenide glasses have been studied using differential scanning calorimetry (DSC) with heating rates 5, 10, 15 and 20 K/min under non-isothermal conditions. Values of various kinetic parameters of crystallization, such as onset crystallization temperature ( T c ), peak crystallization temperature ( T p ), activation energy of crystallization ( E c ), rate constant ( K p ), Hruby number ( K gl ) and the order parameter ( n) have been determined. It was found that activation energy of crystallization and rate constant ( K p ) are minimum at 9 at% In. On the basis of the obtained experimental data the temperature difference ( T c −T g ) and K gl increase with In concentration, which further indicates that 9 at% In glass is most thermally stable in the entire composition range of investigation.

Observation of phase separation in some Se–Te–Sn chalcogenide glasses

Differential scanning calorimeter (DSC) and X-ray diffraction (XRD) techniques were employed here to investigate the glass transition behavior and crystallization kinetics of Se 80− x Te 20Sn x ( x=0.0, 2.5 and 5) alloys, which were prepared by the conventional melt quenching method. Two exothermic peaks have been observed in the DSC scans for the samples that contain Sn. Three crystalline phases (Se 7.68Te 0.32, SnSe and SnTe) were classified after heat treating the Se 77.5 Te 20Sn 2.5 glass at temperature corresponding to the second crystallization peaks for 3 h. All the characteristic temperatures such as glass transition temperature ( T g ), crystallization temperature ( T c ) and crystallization peak temperatures ( T p ) were found to depend on both the heating rate and the composition. This dependence has been used to deduce the activation energy of the glass transition ( E g ), the activation energy of crystallization ( E c ), the Avrami exponent ( n), thermal stability and the fragility index ( F i ).

THE SYSTEM Pd-Sn-Te AT 400 C AND MINERALOGICAL IMPLICATIONS. I. THE BINARY PHASES

The phase relations in the system Pd–Sn–Te were investigated with the evacuated silica tube method, and characterized by electron-microprobe analysis and powder X-ray diffraction. The experimental charges were weighed using pure elements or presynthesized binary phases. The isothermal section was investigated at 400°C. Our experiments revealed the existence of three ternary phases: Pd 67 Sn 11 Te 22 , Pd 72 Sn 16 Te 12 and PdSnTe, unknown as minerals. Two previously reported ternary phases, “Pd 73 Sn 10 Te 17 ” and “Pd 71 Sn 7 Te 22 ”, were not identified in this work. The experiments presented have provided useful data concerning the ranges of solid solutions in the ternary system. The phase PdTe 2 , analogue of merenskyite, dissolves up to 3.5 at.% Sn; the phase PdTe, analogue of kotulskite, dissolves up to 19 at.% Sn, and the phase Pd 20 Te 7 dissolves up to 4 at.% Sn. The phase Pd 2 Sn, analogue of paolovite, dissolves up to 4 at.% Te, and the phase Pd 3 Sn, analogue of atokite, dissolves up to 0.5 at.% Te. At 400°C, the following assemblages were encountered: Sn(liq) + SnTe + PdSn 2 , PdSn 2 + SnTe + PdSn, PdSn + SnTe + Pd 20 Sn 13 , SnTe + Te + PdTe 2 , SnTe + Pd(Te,Sn) 2ss + PdSnTe, SnTe + Pd 20 Sn 13 + PdSnTe, Pd 20 Sn 13 + PdSnTe + Pd(Te,Sn) ss , PdSnTe + Pd(Sn,Te) 2ss + Pd(Te,Sn) ss , Pd 20 Sn 13 + Pd 2 (Sn,Te) ss + Pd(Te,Sn) ss , Pd 2 (Sn,Te) ss + PdTe + Pd 67 Sn 11 Te 22 , PdTe + Pd 67 Sn 11 Te 22 + Pd 3 Te 2 , Pd 67 Sn 11 Te 22 + Pd 3 Te 2 + Pd 9 Te 4 , Pd 67 Sn 11 Te 22 + Pd 9 Te 4 + Pd 20 Te 7 , Pd 2 (Sn,Te) ss + Pd 67 Sn 11 Te 22 + Pd 72 Sn 16 Te 12 , Pd 2 (Sn,Te) ss + Pd 73 Sn 14 Te 13 + Pd 3 (Sn,Te) ss , Pd 72 Sn 16 Te 12 + Pd 67 Sn 11 Te 22 + Pd 20 (Te,Sn) 7ss , Pd 3 (Sn,Te) ss + Pd 72 Sn 16 Te 12 + Pd 20 (Te,Sn) 7ss , Pd 3 (Sn,Te) ss + Pd 20 (Te,Sn) 7ss + Pd 17 Te 4 and Pd 3 Sn + Pd 17 Te 4 + Pd.