|Other names |
3D model (JSmol)
|Molar mass||197.67 g/mol|
|Appearance||steel gray odorless powder|
|Melting point||861 °C (1,582 °F; 1,134 K)|
|Band gap||0.9 eV (indirect), 1.3 eV (direct)|
|Pnma, No. 62|
Std enthalpy of
|H301, H331, H373, H410|
|P260, P261, P264, P270, P271, P273, P301+P310, P304+P340, P311, P314, P321, P330, P391, P403+P233, P405, P501|
|NFPA 704 (fire diamond)|
|Safety data sheet (SDS)||https://www.ltschem.com/msds/SnSe.pdf|
| Tin(II) oxide |
| Carbon monoselenide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
(what is ?)
Tin selenide, also known as stannous selenide, is an inorganic compound with the formula Sn Se. Tin(II) selenide is a typical layered metal chalcogenideas it includes a group 16 anion (Se2−) and an electropositive element (Sn2+), and is arranged in a layered structure. Tin(II) selenide is a narrow band-gap (IV-VI) semiconductor structurally analogous to black phosphorus. It has received considerable interest for applications including low-cost photovoltaics, and memory-switching devices.
Because of its low thermal conductivity as well as reasonable electrical conductivity, tin selenide is one of the most efficient thermoelectric materials.
Tin(II) selenide (SnSe) crystallizes in the orthorhombic structure that derives from a distorted rock-salt structure. It is isomorphous to germanium selenide (GeSe).The unit cell encompasses two inverted layers. Each tin atom is covalently bonded to three neighboring selenium atoms, and each selenium atom is covalently bonded to three neighboring tin atoms. The layers are held together primarily by van der Waals forces. At temperatures above 800 K its structure changes to rock-salt structure.
At pressures above 58 GPa, SnSe acts as a superconductor; this change of conductivity is likely due to a change in the structure to that of CsCl.In recent years, it has become evident that new polymorphs of SnSe exists based upon the cubic and orthorhombic crystal systems, known as π-SnSe (space group: P213, No. 198) and γ-SnSe (space group: Pnma, No. 62)
Tin(II) selenide can be formed by reacting the elements tin and selenium above 350 °C.
Problems with the composition are encountered during synthesis. Two phases exist—the hexagonal SnSe2 phase and the orthorhombic SnSe phase. Specific nanostructures can be synthesized,but few 2D nanostructures have been prepared. Both square SnSe nanostructures and single-layer SnSe nanostructures have been prepared. Historically, phase-controlled synthesis of 2D tin selenide nanostructures is quite difficult.
Sheet-like nanocrystalline SnSe with an orthorhombic phase has been prepared with good purity and crystallization via a reaction between a selenium alkaline aqueous solution and tin(II) complex at room temperature under atmospheric pressure. nm diameter) single-wall carbon nanotubes by heating the nanotubes with SnSe powder in vacuum at 960 °C. Contrary to the bulk SnSe, they have the cubic crystal structure.A few-atom-thick SnSe nanowires can be grown inside narrow (~1
Tin(II) selenide adopts a layered orthorhombic crystal structure at room temperature, which can be derived from a three-dimensional distortion of the NaCl structure. There are two-atom-thick SnSe slabs (along the b–c plane) with strong Sn–Se bonding within the plane of the slabs, which are then linked with weaker Sn–Se bonding along the a direction. The structure contains highly distorted SnSe7 coordination polyhedra, which have three short and four very long Sn–Se bonds, and a lone pair of the Sn2+ sterically accommodated between the four long Sn–Se bonds. The two-atom-thick SnSe slabs are corrugated, creating a zig-zag accordion-like projection along the b axis. The easy cleavage in this system is along the (100) planes. While cooling from its high-temperature, higher symmetry phase (space group Cmcm, #63), SnSe undergoes a displacive (shear) phase transition at ~750–800 K, resulting in a lower symmetry Pnma (#62) space group.Owing to this layered, zig-zag accordion-like structure, SnSe demonstrates low anharmonicity and an intrinsically ultralow lattice thermal conductivity, making SnSe one of the world’s least thermally conductive crystalline materials. The fundamental mechanism of the low thermal conductivity has been elaborated in this “soft” accordion-like layered structure and verified due to a abnormally strong phonon renormalization at room temperature.
Tin(II) selenide may be soon used in energy harvesting. Tin(II) selenide has demonstrated the ability to convert waste heat into electrical energy.SnSe has exhibited the highest thermoelectric material efficiency, measured by the unitless ZT parameter, of any known material (~2.62 at 923 K along the b axis and ~2.3 along the c axis). When coupled with the Carnot efficiency for heat conversion, the overall energy conversion efficiency of approximately 25%. In order for this thermoelectric process to work, a thermoelectric generator must take advantage of the temperature difference experienced by two legs of a thermocouple junction. Each leg is composed of a specific material that is optimized at the operating temperature range of interest. SnSe would serve as the p-type semiconductor leg. Such a material needs to have low total thermal conductivity, high electrical conductivity, and high Seebeck coefficient according to the thermoelectric figure of merit ZT. Even though the record-high efficiency is most likely due to low thermal conductivity of the crystal, the electronic structure may have as important role: SnSe has highly anisotropic valence band structure, which consists of multiple valleys that act as independent channels for very mobile, low effective-mass charge transport within, and heavy-carrier conductivity perpendicular to the layers. While, historically, lead telluride and silicon-germanium have been used, these materials have suffered from heat conduction through the material.
At room temperature, the crystal structure of SnSe is Pnma. However, at ~750 K, it undergoes a phase transition that results in a higher symmetry Cmcm structure. This phase transition preserves many of the advantageous transport properties of SnSe. The dynamic structural behavior of SnSe involving the reversible phase transition helps to preserve the high power factor. The Cmcm phase, which is structurally related to the low temperature Pnma phase, exhibits a substantially reduced energy gap and enhanced carrier mobilities while maintaining the ultralow thermal conductivity thus yielding the record ZT. Because of SnSe’s layered structure, which does not conduct heat well, one end of the SnSe single crystal can get hot while the other remains cool. This idea can be paralleled with the idea of a posture-pedic mattress that does not transfer vibrations laterally. In SnSe, the ability of crystal vibrations (also known as phonons) to propagate through the material is significantly hampered. This means heat can only travel due to hot carriers (an effect that can be approximated by the Wiedemann–Franz law), a heat transport mechanism that is much less significant to the total thermal conductivity. Thus the hot end can stay hot while the cold end remains cold, maintaining the temperature gradient needed for thermoelectric device operation. The poor ability to carry heat through its lattice enables the resulting record high thermoelectric conversion efficiency.The previously reported nanostructured all-scale hierarchical PbTe-4SrTe-2Na (with a ZT of 2.2) exhibits a lattice thermal conductivity of 0.5 W m−1 K−1. The unprecedentedly high ZT ~2.6 of SnSe arises primarily from an even lower lattice thermal conductivity of 0.23 W m−1 K−1. However, in order to take advantage of this ultralow lattice thermal conductivity, the synthesis method must result in macroscale single crystals as p-type polycrystalline SnSe has been shown to have a significantly reduced ZT. Enhancement in the figure of merit above a relatively high value of 2.5 can have sweeping ramifications for commercial applications especially for materials using less expensive, more Earth-abundant elements that are devoid of lead and tellurium (two materials that have been prevalent in the thermoelectric materials industry for the past couple decades).
Tin selenides may be used for optoelectronic devices, solar cells, memory switching devices,and anodes for lithium-ion batteries.
Tin(II) selenide has an additional use as a solid-state lubricant, due to the nature of its interlayer bonding.However, it is not the most stable of the chalcogenide solid-state lubricants, as tungsten diselenide has much weaker interplanar bonding, is highly chemically inert and has high stability in high-temperature, high-vacuum environments.
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. Its conducting properties may be altered in useful ways by introducing impurities ("doping") into the crystal structure. When two differently doped regions exist in the same crystal, a semiconductor junction is created. The behavior of charge carriers, which include electrons, ions, and electron holes, at these junctions is the basis of diodes, transistors, and most modern electronics. Some examples of semiconductors are silicon, germanium, gallium arsenide, and elements near the so-called "metalloid staircase" on the periodic table. After silicon, gallium arsenide is the second-most common semiconductor and is used in laser diodes, solar cells, microwave-frequency integrated circuits, and others. Silicon is a critical element for fabricating most electronic circuits.
The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by , , or .
Thermoelectric cooling uses the Peltier effect to create a heat flux at the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other, with consumption of electrical energy, depending on the direction of the current. Such an instrument is also called a Peltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC) and occasionally a thermoelectric battery. It can be used either for heating or for cooling, although in practice the main application is cooling. It can also be used as a temperature controller that either heats or cools.
Thermoelectric materials show the thermoelectric effect in a strong or convenient form.
A semimetal is a material with a very small overlap between the bottom of the conduction band and the top of the valence band. According to electronic band theory, solids can be classified as insulators, semiconductors, semimetals, or metals. In insulators and semiconductors the filled valence band is separated from an empty conduction band by a band gap. For insulators, the magnitude of the band gap is larger than that of a semiconductor. Because of the slight overlap between the conduction and valence bands, semimetals have no band gap and a negligible density of states at the Fermi level. A metal, by contrast, has an appreciable density of states at the Fermi level because the conduction band is partially filled.
Skutterudite is a cobalt arsenide mineral containing variable amounts of nickel and iron substituting for cobalt with the ideal formula CoAs3. Some references give the arsenic a variable formula subscript of 2–3. High nickel varieties are referred to as nickel-skutterudite, previously chloanthite. It is a hydrothermal ore mineral found in moderate to high temperature veins with other Ni-Co minerals. Associated minerals are arsenopyrite, native silver, erythrite, annabergite, nickeline, cobaltite, silver sulfosalts, native bismuth, calcite, siderite, barite and quartz. It is mined as an ore of cobalt and nickel with a by-product of arsenic.
A clathrate is a chemical substance consisting of a lattice that traps or contains molecules. The word clathrate is derived from the Latin clathratus, meaning ‘with bars, latticed’. Most clathrate compounds are polymeric and completely envelop the guest molecule, but in modern usage clathrates also include host–guest complexes and inclusion compounds. According to IUPAC, clathrates are inclusion compounds "in which the guest molecule is in a cage formed by the host molecule or by a lattice of host molecules." The term refers to many molecular hosts, including calixarenes and cyclodextrins and even some inorganic polymers such as zeolites.
Heusler compounds are magnetic intermetallics with face-centered cubic crystal structure and a composition of XYZ (half-Heuslers) or X2YZ (full-Heuslers), where X and Y are transition metals and Z is in the p-block. The term derives from the name of German mining engineer and chemist Friedrich Heusler, who studied such a compound (Cu2MnAl) in 1903. Many of these compounds exhibit properties relevant to spintronics, such as magnetoresistance, variations of the Hall effect, ferro-, antiferro-, and ferrimagnetism, half- and semimetallicity, semiconductivity with spin filter ability, superconductivity, topological band structure and are actively studied as Thermoelectric materials. Their magnetism results from a double-exchange mechanism between neighboring magnetic ions. Manganese, which sits at the body centers of the cubic structure, was the magnetic ion in the first Heusler compound discovered. (See the Bethe–Slater curve for details of why this happens.)
Lead selenide (PbSe), or lead(II) selenide, a selenide of lead, is a semiconductor material. It forms cubic crystals of the NaCl structure; it has a direct bandgap of 0.27 eV at room temperature. A grey solid, it is used for manufacture of infrared detectors for thermal imaging. The mineral clausthalite is a naturally occurring lead selenide.
Bismuth telluride is a gray powder that is a compound of bismuth and tellurium also known as bismuth(III) telluride. It is a semiconductor, which, when alloyed with antimony or selenium, is an efficient thermoelectric material for refrigeration or portable power generation. Bi2Te3 is a topological insulator, and thus exhibits thickness-dependent physical properties.
Lead telluride is a compound of lead and tellurium (PbTe). It crystallizes in the NaCl crystal structure with Pb atoms occupying the cation and Te forming the anionic lattice. It is a narrow gap semiconductor with a band gap of 0.32 eV. It occurs naturally as the mineral altaite.
Tin telluride is a compound of tin and tellurium (SnTe); is a IV-VI narrow band gap semiconductor and has direct band gap of 0.18 eV. It is often alloyed with lead to make lead tin telluride, which is used as an infrared detector material.
Silver selenide (Ag2Se) is the reaction product formed when selenium toning analog silver gelatine photo papers in photographic print toning. The selenium toner contains sodium selenite (Na2SeO3) as one of its active ingredients, which is the source of the selenide (Se2−) anion combining with the silver in the toning process.
A thermoelectric generator (TEG), also called a Seebeck generator, is a solid state device that converts heat flux directly into electrical energy through a phenomenon called the Seebeck effect. Thermoelectric generators function like heat engines, but are less bulky and have no moving parts. However, TEGs are typically more expensive and less efficient.
The indium chalcogenides include all compounds of indium with the chalcogen elements, oxygen, sulfur, selenium and tellurium. (Polonium is excluded as little is known about its compounds with indium). The best-characterised compounds are the In(III) and In(II) chalcogenides e.g. the sulfides In2S3 and InS.
This group of compounds has attracted a lot of research attention because they include semiconductors, photovoltaics and phase-change materials. In many applications indium chalcogenides are used as the basis of ternary and quaternary compounds such as indium tin oxide, ITO and copper indium gallium selenide, CIGS.
Tin(II) sulfide is a chemical compound of tin and sulfur. The chemical formula is SnS. Its natural occurrence concerns herzenbergite (α-SnS), a rare mineral. At elevated temperatures above 905 K, SnS undergoes a second order phase transition to β-SnS (space group: Cmcm, No. 63). In recent years, it has become evident that a new polymorph of SnS exists based upon the cubic crystal system, known as π-SnS (space group: P213, No. 198).
As the devices continue to shrink further into the sub-100 nm range following the trend predicted by Moore’s law, the topic of thermal properties and transport in such nanoscale devices becomes increasingly important. Display of great potential by nanostructures for thermoelectric applications also motivates the studies of thermal transport in such devices. These fields, however, generate two contradictory demands: high thermal conductivity to deal with heating issues in sub-100 nm devices and low thermal conductivity for thermoelectric applications. These issues can be addressed with phonon engineering, once nanoscale thermal behaviors have been studied and understood.
Oxyselenides are a group of chemical compounds that contain oxygen and selenium atoms. Oxyselenides can form a wide range of structures in compounds containing various transition metals, and thus can exhibit a wide range of properties. Most importantly, oxyselenides have a wide range of thermal conductivity, which can be controlled with changes in temperature in order to adjust their thermoelectric performance. Current research on oxyselenides indicates their potential for significant application in electronic materials.
Molybdenum(IV) telluride, molybdenum ditelluride or just molybdenum telluride is a compound of molybdenum and tellurium with formula MoTe2, corresponding to a mass percentage of 27.32% molybdenum and 72.68% tellurium. It can crystallise in two dimensional sheets which can be thinned down to monolayers that are flexible and almost transparent. It is a semiconductor, and can fluoresce. It is part of a class of materials called transition metal dichalcogenides. As a semiconductor the band gap lies in the infrared region. This raises the potential use as a semiconductor in electronics or an infrared detector.
Mercouri Kanatzidis is a Charles E. and Emma H. Morrison Professor of chemistry and professor of materials science and engineering at Northwestern University and Senior Scientist at Argonne National Laboratory.