Article

A Conceptional Approach to Materials for Resistivity Switching and Thermoelectrics

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  • Deutsche ACCUmotive GmbH & Co KG
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Abstract

Recently silver(I)-(poly)chalcogenides have received special interest in energy conversion materials because of their thermoelectric and resistivity switching properties. In order to understand these features, a new topological principle has been developed, which is an useful tool to plan new synthesis strategies and to vary functional properties. It has been shown that anion substitution is powerful tool to tune the physical properties in terms of a thermoelectric performance optimization. Herein we report on the recently introduced substance class of silver(I)-(poly)chalcogenidehalides and the well-established class of silver(I)-chalcogenidehalides. We focus our report on the electrochemical behaviour of all known silver-(poly)telluridehalides Ag10Te4Br3, Ag23Te12Br, Ag20Te10BrI,Ag5Te2Cl and selected substituted phases.

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... The change in the magnitude of Seebeck during p-n-p type conduction switching in Ag 10 Te 4 Br 3 , AgBiSe 2 , AgCuS, and Ag 10 Te 4 Br 2.6 Cl 0.4 are 1400, 730, 1760 and 1800 mV K À1 , respectively. 2,6,17,23 Temperatures of the p-n-p type transition in several compounds are given in Table 1. ...
... 43,44 In order to shift the temperature driven p-n-p type conduction switching to an applicable temperature, various cationic/anioinic substitutions in Ag 10 Te 4 Br 3 were investigated. 23 Although little shift in transition temperature was observed with 2 mol% iodine doping (Ag 10 Te 4 Br 2.8 I 0.2 ), but the jump in the Seebeck coefficient was much smaller compared to that of pristine Ag 10 Te 4 Br 3 (Fig. 5). 23 Interestingly, the solid solution Ag 10 Te 4 Br 2.6 Cl 0.4 shows a significant jump in the Seebeck coefficients with a DS B 1800 mV K À1 (Fig. 1 and 5). ...
... 23 Although little shift in transition temperature was observed with 2 mol% iodine doping (Ag 10 Te 4 Br 2.8 I 0.2 ), but the jump in the Seebeck coefficient was much smaller compared to that of pristine Ag 10 Te 4 Br 3 (Fig. 5). 23 Interestingly, the solid solution Ag 10 Te 4 Br 2.6 Cl 0.4 shows a significant jump in the Seebeck coefficients with a DS B 1800 mV K À1 (Fig. 1 and 5). 23 Sulphur and selenium substitution on the Te sublattice resulted in the complete disappearance of the p-n-p conduction switching (Fig. 5), 23 because the Peierls distortion within the covalently bonded Te-substructure was disturbed effectively by a lightered homologue, sulphur or selenium. ...
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Modern technological inventions have been going through a “renaissance” period. Development of new materials and understanding of fundamental structure-property correlations are the important steps to move further for advanced technologies. In modern technologies, inorganic semiconductors are the leading materials which are extensively used for different applications. In the current perspective, we present discussion on an important class of material that show fascinating p-n-p type conduction switching, which can have potential application in diode or transistor devices that operate reversibly on temperature or voltage change. We highlight the key concepts, present the current fundamental understanding and show the latest developments in the field of p-n-p type conduction switching. Finally, we point out the major challenges and opportunities in this field.
... 12,13 Conductivity type can also be inverted upon structural phase transitions, for example, under variation either in pressure 5,7,14 or in temperature. [15][16][17][18][19][20] Note that doping and implantation result in irreversible changes in electronic transport properties, whereas variations linked to pressure-or temperature-driven structural phase transitions are often reversible. However, in the latter case, a multiple cycling across phase transitions can severely damage specimens. ...
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Under applied high pressure, the electronic, optical, structural, and other properties of narrow-bandgap telluride semiconductors are subjected to dramatic changes. They can include, for instance, structural and electronic topological transitions. In this work, we investigated the electronic properties of single crystals of three families of tellurides, namely, HgTe, PbTe, and Bi2Te3 by measurements of the thermoelectric power (the Seebeck coefficient) and electrical resistance under high pressure up to 10 GPa. The applied pressure led to spectacular variations in the electronic transport of all three tellurides. We addressed these effects to electronic topological transitions that could be driven by significant narrowing of the bandgaps in the normal-pressure phases of these compounds. In particular, at about 1 GPa, we observed an n-p switching in the conductivity of HgTe, which was well reproducible under multiple pressure cycling. In contrast, in PbTe, we found that an electronic topological transition irreversibly turns the conductivity from p- to n-type. An electronic topological Lifshitz transition in p-type Bi2Te3 crystals with a low carrier concentration enhanced the n-type conductivity in a narrow pressure region about 2–3 GPa and resulted in a double p–n–p conductivity inversion. An irreversible p–n conductivity switching in p-type Bi2Te3 happened already on decompression from a high-pressure phase from about 8 GPa. The stress-controlled p–n inversions of the electrical conductivity in these industrially important telluride materials can potentially find emergent applications in micro- and nanoelectronics.
... Since semiconductor elements are the basis of modern electronics, both novel materials and alternative methods, which could effectively tune their optoelectronic properties, are always in much demand. 62 Variation in the temperature can induce drastic changes in electronic transport properties (e.g., p-n switching), for example, in Ag 10 Te 4 Br 3 , 63 AgBiSe 2 , 64 AgCuS, 65 Ag 10 Te 4 Br 2.6 Cl 0.4 , 66 and in La x Sr 2−x TiFeO 6 perovskites. 67 However, this approach can only be used to a limited extent in practical micro-or nanoelectronic devices. ...
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Silicon, germanium and their alloys are classical semiconductors that play an important role in fundamental sciences and are the basis for modern microelectronics, optoelectronics, energy conversion, and other applications. The thermoelectric power (Seebeck coefficient) of p- and n-type materials in combination with the electrical and thermal conductivities characterizes the efficiency of thermal-to-electric energy conversion. In this work we experimentally show how one can effectively control the thermoelectric power of silicon-germanium alloys using an applied high pressure. We measured the Seebeck coefficient and the electrical resistance for several Si1−xGex crystals with different compositions under applied high pressure in (i) their original semiconductor cubic-diamond structure, (ii) across a phase transition to a metal phase at about 9–13 GPa, and (iii) across phase transformations to different metastable phases on pressure release. These studies were carried out for several pressurization and decompression cycles. The Si–Ge samples were examined by X-ray diffraction and Raman spectroscopy. After the high-pressure cycling the Si–Ge samples transformed into two metastable phases, namely, a cubic bc8 phase (Si-III) with a p-type electrical conductivity in the Si-dominant samples, and a tetragonal st12 phase (Ge-III) in the Ge-dominant alloys, whose conductivity type depended on the Si content. The dramatic pressure-driven changes in the thermoelectric power of Si–Ge crystals we found suggest that these semiconductors are promising for use in various stress-controlled electronic junctions, such as switches, p–n diode elements, n–p–n (p–n–p) transistors, and multi-layer heterostructures with alternating types of electrical conductivity.
... Although these Ag/Cu based chalcogenide exhibit interesting p-n-p switching but their conduction is dominated by mobile cations(Ag þ /Cu þ ) in the superionic phase therefore their stability with temperature is an issue of concern. [7] Hence an electronic semiconductor exhibiting conduction switching can be a good choice for application. Chalcogenide such as bismuth telluride based alloys are electronic semiconductor and they are extensively used as conventional thermoelectric material for converting waste heat into electrical energy in the temperature range of 300 C. [8][9] Bismuth telluride is a V-VI chalcogenide compounds with narrow band gap semiconductor of 0.16-0.3 ...
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Bismuth telluride based alloys are electronic semiconductors, which exhibit n‐ or p‐type conduction due to the formation of Te vacancies or antisite defects, i.e., substitution of Bi on Te site or vice versa. Here, it is demonstrated that the temperature dependent Seebeck coefficient of Bi2Te2.7Se0.3 exhibits a reversible change in conduction from p‐ to n‐type at temperatures >487 K without exhibiting any structural transformation. The detailed characterization revealed that conversion of BiTe/Se antisite defects into Te vacancies is responsible for the p–n transition. The observed p–n transition makes Bi2Te2.7Se0.3 an ideal candidate for temperature controlled electronic switches. Bismuth telluride based alloys usually exhibit n‐ or p‐type conduction due to Te vacancies or due to the formation of Bi vacancies or anitisite defects, i.e., Bi substitution on Te sites or vice versa. The temperature dependent Seebeck coefficient of Bi2Te2.7Se0.3 exhibits a reversible change in conduction from p‐ to n‐type at temperatures >487 K without exhibiting any structural transformation. The conversion of BiTe/Se antisite defects into Te vacancies is responsible for p to n transition of Bi2Te2.7Se0.3.
... Previously such p-n type conduction switching assis- ted large change in thermopower was reported in the literature for few chalcogenide-based compounds, only in the last five years. But for the very first time it was observed in perovskite-based oxide materials and also the change in thermopower was larger than the previously reported results, as shown in the comparison 20,21,[98][99][100][101][102] bar chart in Fig. 12. Such p-n switching coupled with a large change in thermopower in a single material as a result of only temperature change, opens up a new avenue for developing novel high-temperature diodes, thyristors, sensors, switches, thermistors, etc. ...
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... In Ag 10 Te 4 Br 3 , a similar p−n−p switching behavior has been attributed to a charge density wave (CDW) linked to a Peierls transition 15 that influences the electronic density of states close to the Fermi level, and it has been suggested that this thermopower modulation could be used to develop improved TE materials. 16 A strong anomaly was also observed in the temperature dependence of the thermal diffusivity ( Figure S7). ...
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Herein we report the structural, thermal and physical properties of Ag5Te2−ySeyCl (y=0–0.7). Polymorphic Ag5Te2Cl (y=0) is an ion conductor with two reversible phase transitions at 241 and 334 K. While the monoclinic room temperature β- and the low temperature γ-phase show conductivities below σ=10−3Ω−1cm−1, the tetragonal high temperature α-phase is a promising conductor for electronic devices with conductivities up to 10−1Ω−1cm−1 in addition to high moisture and photo stability. The α–β-phase transition temperature of ion conducting Ag5Te2Cl can be lowered by partial substitution of tellurium by selenium. From differential thermal analysis (DTA) and differential scanning calorimetry (DSC) a linear decrease of the α–β-phase transition temperature with increasing compositional parameter y to a minimum transition temperature of 239 K was observed for Ag5Te1.3Se0.7Cl. Phases up to a maximum selenium content of y=0.7 were stabilized by preservation of the β- and α-Ag5Te2Cl structure types. Ag5Te2−ySeyCl (y=0–0.9) phases were characterised by powder X-ray diffraction (XRD) at room temperature. The stabilization of the α-Ag5Te2Cl structure type in Ag5Te2−ySeyCl around room temperature results in an increase of conductivity of more than 2 orders of magnitude compared to the ternary phase. Conductivity of up to σ=5.1×10−2Ω−1cm−1 (314 K, α-Ag5Te1.6Se0.4Cl) was observed by impedance spectroscopy. In the range from room temperature down to 239 K any transition temperature can be chosen by simply varying the composition.
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The distinction between valence electrons and essentially inactive core electrons is the basis of many classifying concepts in chemistry. However, it has recently been recognized that this is an oversimplification and should, at least in some areas of chemistry, be modified. Many cases are known where cations with closed d10 configurations are subject to homoatomic interactions that influence structure and properties. A characteristic and surprisingly uniform structural feature (e.g., of a number of compounds containing monovalent coinage metals) is a clusterlike assembly of d10 cations that corresponds in geometry and bond lengths to fragments of the metal structures themselves. Further evidence for a special type of bonding in such compounds is provided by their physical properties; for example, the absorption in the UV/VIS region shows a drastic redshift and the compounds are often conductors or semiconductors. The d electrons in such cases have obviously lost their pure “core” nature. All bonding models so far proposed for such systems involve mixing of higher orbitals.
Article
Thermoelectric power generation is foreseen to play a much larger role in the near future, considering the need for alternative energies because of declining natural resources as well as the increasing efficiency of thermoelectric materials. The latter is a consequence of the discoveries of new materials as well as of improvements of established materials by, for example, nanostructuring or band structure engineering. Within this review, two major classes of high-temperature thermoelectrics are presented: clathrates formed by silicides and germanides, and complex antimonides including but not limited to the filled skutterudites. The clathrates and the skutterudites are cage compounds that exhibit low thermal conductivity, reportedly related to the rattling effect of the guest atoms, whereas the other antimonides achieve low thermal conductivity via defects or simply via the high complexity of their crystal structures.
Article
Systematic examinations for new phases on the quasi-binary section AgX−Ag2Q (with X = halide and Q = chalcogenide) led to the exploration of the three new compounds Ag19Te6Br7, Ag19Te6Br5.4I1.6, and Ag19Te5SeBr7. All of them crystallize in new structure types with rigid anion and highly disordered silver substructures. A peritectic decomposition to the binary halides and chalcogenides and Ag23Te12Br was observed for each compound between 693 and 719 K. Polymorphism, a common feature for solid state ion conductors, was found for Ag19Te6Br7. Impedance spectroscopic investigations showed high conductivities (up to σ = 1.1 × 10 −2 Ω−1 cm−1, 323 K, Ag19Te6Br5.4I1.6) and low activation energies (Ea = 0.19 eV, α-Ag19Te6Br7) at room temperature. A topological description of the rigid and complex anion substructure was used to classify the three different structures. Linearly arranged nets of anions, separated from each other by the disordered silver ions, corrugate under partial substitution of either the halide or chalcogenide ions. The topological approach is a fundamental tool to understand the structure property relations in more detail.
Article
Thermoelectric and phase analytical measurements were performed to investigate the physical properties of trimorphic Ag5Te2Cl. The material is a mixed electron/silver ion conductor featuring drastic property changes during a silver order/disorder phase transition at 334 K. The transition is characterized by a jump in the total electric conductivity by 2 orders of magnitude directly affecting the electric and thermoelectric properties. Silver ions are arranged in well-defined strands along the crystallographic c-axis characterized by a set of not fully occupied sites. Heat capacity measurements show a large effect, whereas the thermopower and thermal diffusivity drop significantly at the temperature of transition. Right after the transition, an attractive d10−d10 interaction within the disordered silver substructure occurs affecting the c-lattice parameter upon heating. Due to this interaction a modulation of the electronic structure and the thermoelectric properties can be observed which have been investigated in detail. While the thermopower stays low with increasing temperature the thermal diffusivity relaxes fast to values before the transition. At 355 K, the thermopower starts rising again, which is consistent with a small effect in the heat capacity and a reduction of the c-lattice parameter upon heating. Further heating leads to a reduction of the d10−d10 interactions and a drastic increase in the thermopower. The observed phenomenon must be regarded as a new example of a compound following the recently discovered concept of low-dimensional partially covalent-bonded structure units that can positively influence thermoelectric properties in bulk materials. Ag5Te2Cl is the first example where mobile d10 ions interact to create low-dimensional partially covalent-bonded subunits in a solid, which then leads to a switching of thermoelectric and electronic properties. The system shows very low thermal conductivities between 0.19 W m−1 K−1 and 0.60 W m−1 K−1 in the temperature range 298 to 500 K, reaching a maximal ZT value of 0.033 at high temperatures.
Article
Ag10Te4Br3 is the first representative of an M(group 11) (poly)chalcogenide halide with covalently bonded [Te2]2- units and isolated Te2- ions. It represents a new class of materials located between M(group 11) chalcogen halides, characterized by covalently bonded chalcogen structure motives, on the one hand and chalcogenide halides, consisting of isolated chalcogenide ions, on the other. A high silver mobility on distinct silver layers was observed for orthorhombic Ag10Te4Br3, resulting in a pronounced 1D silver mobility at room temperature. The covalent regions of the chalcogen substructure account for the lowest activation energies, determined after a detailed analysis of the silver joint probability density functions (jpdf). Impedance spectroscopic measurements were performed in order to substantiate the results from jpdf analyses. Ag10Te4Br3 is an excellent conductor, with conductivities on the same order of magnitude as β-Ag3SX (X = I, Br) or glassy silver chalcogenide halides. The occurrence of the [Te2]2- dumbbell was substantiated by Raman spectroscopy.
Article
Single-crystal structure determinations at room temperature and elevated temperatures were carried out on the silver ion conductor Ag5Te2Cl, and the hitherto unknown structure of the room-temperature phase (β-Ag5Te2Cl) was determined. Ion pathways are discussed for the room- and high-temperature phase by analyzing the joint probability density functions. Main transport pathways at different temperatures were worked out to obtain detailed insight into the movement of the silver atoms in this material. Ag5Te2Cl is an excellent 1D ionic conductor having a pronounced silver mobility along complex silver columns. Conductivities are σ = 1.51 × 10-3 Ω-1 cm-1 at 323 K and σ = 4.30 × 10-1 Ω-1 cm-1 at 469 K. With use of a nonharmonic description of the silver distribution of the high-temperature phase, a promising structure model has been derived for the room-temperature phase. β-Ag5Te2Cl can be regarded as an intermediate phase between the disordered high- and the ordered low-temperature phase, showing an almost ordered silver distribution in addition to a slightly different arrangement of the anionic substructure.
Article
X-ray powder diffraction, EDX and DSC measurements were performed in order to determine the structural and thermal properties of the solid solutions of Ag23Te12Cl1–xBrx, Ag23Te12Br1–yIy and Ag23Te12Cl1–zIz. A complete solid solution exists between the two ternary end members Ag23Te12Cl and Ag23Te12Br, whereas the substitution of bromine by iodine can only be observed up to y = 0.3 in Ag23Te12Br1–yIy under thermodynamically controlled synthesis conditions. Even chlorine can be partially substituted by small amounts of iodine up to a certain extend. Temperature dependent single crystal structure determinations of crystals with the nominal composition Ag23Te12Cl0.95I0.05 substantiated the significant influence of the iodine intake on the lattice parameters of the pseudo-tetragonal orthorhombic system, especially at low temperatures. A systematic deviation from the 1:1 ratio of the a and b lattice parameter (pseudo-tetragonal ratio) was observed upon cooling, which could not be detected in the case of the ternary compounds. X-ray powder diffraction experiments gave a first hint on the non-stoichiometry of this set of materials and all compounds show peritectic decomposition to binary phases at temperatures slightly above 680 K.
Article
Recent progress in the field of silver(I)-chalcogenide halides and silver(I)-polychalcogenide halides led to the discovery of a reasonable number of new phases, solid solutions and even a new substance class of materials with favorable electronic and thermoelectric properties. Most of these new compounds are characterized by a pronounced ion mobility, polymorphism, and complex structures, which result in severe problems during the structure solution, the refinement, and even the description of the crystal structures. Herein we report on a very simple but effective building principle and a topological structure approach, which are both based on the separate description of anion substructures and the introduction of discrete building blocks. Such a topological principle helps to understand the complex structural relations and allows one to discuss all known chalcogenide and polychalcogenide halides in a continuous sequence of compounds. Following this principle it is possible to understand physical properties and to predict new phases in the system.
Article
The structures, thermal and physical properties of ion conducting polymorphic Ag5Te2Cl1−xBrx and Ag5Te2−ySyCl have been investigated. A maximum substitution degree of x = 0.65 and y = 0.3 was derived from X-ray powder diffraction. Mixtures of silver halides, silver chalcogenides and Ag3TeBr were observed for higher substitution degrees. Both silver chalcogenide halide systems show a Vegard type behaviour. Single crystal structure determinations of selected materials were performed at different temperatures to analyse the silver distribution in the tetragonal high temperature α- and the monoclinic room temperature β-phases. After non-harmonic refinement of the silver positions detailed joint probability density function analysis (jpdf) and determination of one particle potentials (opp) were carried out to investigate the diffusion pathways and bottlenecks of ion transport for those materials. A preferred anisotropic ion transport along the diffusion pathways for the α- and 1D zig-zag diffusion pathways for the β-phases were found. α–β and β-γ phase transitions were determined by DSC and DTA methods and conductivities were measured using temperature dependent impedance spectroscopy. The substitution of tellurium by sulphur lowered the α–β phase transition from 334 K (Ag5Te2Cl) to 270 K (Ag5Te1.8S0.2Cl) while the opposite trend was found for the Ag5Te2Cl1−xBrx phases. The α–β phase transition of Ag5Te2Cl0.35Br0.65 at 343 K represents the highest transition observed for the silver chalcogenide halides under discussion. Total conductivities of approx. 1 Ω−1 cm−1 (α-Ag5Te2Cl0.5Br0.5) and 0.24 Ω−1 cm−1 (α-Ag5Te1.8S0.2Cl) at 473 K were found being slightly higher (Br) and lower (S) than the conductivity observed for α-Ag5Te2Cl. A conductivity jump of more than two orders of magnitude, related to the α–β phase transitions, within the temperature range from 270 to 343 K is adjustable by simple variation of the composition and is therefore an extraordinary feature of these materials. The total conductivity is linearly correlated to the volume of the anion substructure and can be varied within more than half an order of magnitude.
Article
A solid solution of the general formula Sn24P19.3ClyI8−y (y ≤ 0.8) with a crystal structure of the clathrate-I type (cubic, ) was prepared by a standard ampoule technique and found to be isostructural to the previously discovered Sn24P19.3BrxI8−x (x = 0–8). The unit cell parameter linearly decreases from 10.954(1) Å for y = 0 to 10.933(1) Å for y = 0.8. Sn24P19.3ClyI8−y (y ≤ 0.8) and Sn24P19.3BrxI8−x (x = 0–8) reveal a non-uniform communal distribution of the halogen atoms inside the cages of different size formed in the clathrate framework. The halogen atoms of smaller size (chlorine for Sn24P19.3ClyI8−y and bromine for Sn24P19.3BrxI8−x) preferentially occupy the smaller 20-vertex cages. Thereby the chlorine atoms do not show a complete segregation in the smaller cages, but mix with the iodine atoms in both types of cages. The magnetic and thermoelectric properties for Sn24P19.3ClyI8−y (y ≤ 0.8) as well as for Sn24P19.3BrxI8−x (x = 0–8) were investigated. Both solid solutions are diamagnetic semiconductors as expected for Zintl phases. The core diamagnetism of the guest atoms contributes primarily to the diamagnetic susceptibility of the compounds. The band gap in the case of Sn24P19.3BrxI8−x (x = 0–8) varies from 0.03 eV to 0.14 eV and appears to be a linear function of the guest halogen atom ratios. The lowest value of thermal conductivity, 0.5 W m−1 K−1 at room temperature, is observed for Sn24P19.3Br2I6 featuring the almost random distribution of the guest bromine and iodine atoms.Graphical abstract
Article
Thermoelectric devices can convert heat into useful electricity with no moving parts. Considerable progress has been made in improving the efficiency of these devices over the past 15 years. The key ideas responsible for most of this progress will be examined using specific examples. Recent improvements in thermoelectric efficiency appear to be dominated by a reduction in the lattice thermal conductivity. This reduction is accomplished by the careful introduction of 0.1–5-nm sized “objects” that effectively scatter acoustic phonons without significantly affecting electronic transport. Future research directions will be discussed.
Article
Controlling simultaneously the electric and thermal properties of materials can lead to very efficient thermoelectric devices. Advances following different routes were highlighted at a recent conference.
Article
Zintl phases and related compounds are promising thermoelectric materials; for instance, high zT has been found in Yb_(14)MnSb_(11), clathrates, and the filled skutterudites. The rich solid-state chemistry of Zintl phases enables numerous possibilities for chemical substitutions and structural modifications that allow the fundamental transport parameters (carrier concentration, mobility, effective mass, and lattice thermal conductivity) to be modified for improved thermoelectric performance. For example, free carrier concentration is determined by the valence imbalance using Zintl chemistry, thereby enabling the rational optimization of zT. The low thermal conductivity values obtained in Zintl thermoelectrics arise from a diverse range of sources, including point defect scattering and the low velocity of optical phonon modes. Despite their complex structures and chemistry, the transport properties of many modern thermoelectrics can be understood using traditional models for heavily doped semiconductors.
Article
L'appareil décrit dans le texte est conçu pour mesurer le pouvoir thermoélectrique de monocristaux de forte résistivité (≃ 1010 Ω cm) entre 4 et 300 K. Il permet d'effectuer des mesures sur des échantillons de faibles dimensions (< 0,5 mm). Le dispositif a été testé sur un monocristal de magnétite de composition stœchiométrique. Bien que non construit pour, il est capable de mesurer le coefficient de Seebeck d'échantillons métalliques pour lesquels α < 10 μV/°C.
Article
Two new silver (poly)chalcogenide halides, Ag23Te12Cl and Ag23Te12Br, were characterized by powder X-ray phase analysis, energy dispersive X-ray analysis, and crystal structure determinations at various temperatures. Thermal analyses of both compounds and electrochemical measurements for the bromide completed the investigation. The compounds Ag23Te12X (X = Cl, Br) are isostructural and crystallize orthorhombically (space group Pnnm, Z = 4) as systematic twins. The lattice parameter values derived from X-ray powder data were a = 21.214(2) A, b = 21.218(2) A, c = 7.7086(7) A, and V = 3469.8(6) A (3) for Ag23Te12Cl at 293 K and a = 21.170(1) A, b = 21.170(1) A, c = 7.7458(5) A, and V = 3471.4(4) A (3) for Ag23Te12Br at 298 K. An enhanced silver ion mobility was revealed by impedance spectroscopy investigations. No phase transitions were observed in the temperature range 100-750 K. These two silver(I) (poly)chalcogenide halides are the second set of representatives of a new class of coinage-metal (poly)chalcogenide halides in which both covalently bonded [Te2](2-) dumbbells and ionically bonded Te(2-) anions appear.