Samarium monochalcogenides

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Samarium monochalcogenides are chemical compounds with the composition SmX, where Sm stands for the lanthanide element samarium and X denotes any one of three chalcogen elements, sulfur, selenium or tellurium, resulting in the compounds SmS, SmSe or SmTe. In these compounds, samarium formally exhibits oxidation state +2, whereas it usually assumes the +3 state, resulting in chalcogenides with the chemical formula Sm2X3.

Contents

Synthesis

Single crystals or polycrystals of samarium monochalcogenides can be obtained by reacting the metal with sulfur, selenium or tellurium vapors at high temperature. [1] Thin films can be obtained by magnetron sputtering [2] or electron beam physical vapor deposition, that is bombardment of samarium metal target with electrons in and appropriate gas atmosphere (e.g. hydrogen disulfide for SmS). [3]

Properties

FormulaLattice constant
nm [1] 		Resistivity
Ohm·cm		 Band gap
eV
SmS0.5970.001–0.010.15
SmSe0.620~30000.45
SmTe0.6594~10000.65

Samarium monochalcogenides are black semiconducting solids with rock-salt cubic crystal structure. Application of moderate hydrostatic pressure converts them into metals. Whereas the transition is continuous and occurs at about 45 and 60 kbar in SmSe and SmTe, respectively, it is abrupt in SmS and requires only 6.5 kbar. Similar effect is observed in monochalcogenides of another lanthanide, thulium. [4] This results in spectacular change in color from black to golden yellow when scratching or mechanically polishing SmS. [3] [5] The transition does not change the crystal structure, but there is a sharp decrease (about 15%) [6] in the crystal volume. A hysteresis is observed, that is when the pressure is released, SmS returns to semiconducting state at much lower pressure of about 0.5 kbar. [1]

Not only color and electrical conductivity, but also other properties change in samarium monochalcogenides with increasing pressure. Their metallic behavior results from the decreasing band gap, which amounts at zero pressure to 0.15, 0.45 and 0.65 eV in SmS, SmSe and SmTe, respectively. [1] [4] At the transition pressure (6.5 kbar in SmS) the gap is still finite and the low resistivity originates from thermally activated generation of carriers across a narrow band gap. The gap collapses at about 20 kbar when SmS becomes a true metal. At this pressure, the material also changes from paramagnetic to a magnetic state. [6]

The semiconductor-metal transition in samarium monochalcogenides requires application of pressure or presence of intrinsic stress, for example in thin films, and the reverse changes occur upon release of this stress. Such release can be triggered by various means, such as heating to about 200 °C [3] or irradiation with a pulsed, high-intensity laser beam. [2] [7]

Potential applications

The change in electrical resistivity in samarium monochalcogenides can be used in a pressure sensor or in a memory device triggered between a low-resistance and high-resistance state by external pressure, [8] and such devices are being developed commercially. [9] Samarium monosulfide also generates electric voltage upon moderate heating to about 150 °C that can be applied in thermoelectric power converters. [10]

Related Research Articles

The lanthanide or lanthanoid series of chemical elements comprises the 14 metallic chemical elements with atomic numbers 57–70, from lanthanum through ytterbium. Lutetium is also sometimes considered a lanthanide, despite being a d-block element and a transition metal. These elements are often collectively known as the rare-earth elements or rare-earth metals.

<span class="mw-page-title-main">Samarium</span> Chemical element, symbol Sm and atomic number 62

Samarium is a chemical element; it has symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of samarium(II) are also known, most notably the monoxide SmO, monochalcogenides SmS, SmSe and SmTe, as well as samarium(II) iodide.

<span class="mw-page-title-main">Tellurium</span> Chemical element, symbol Te and atomic number 52

Tellurium is a chemical element; it has symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally found in its native form as elemental crystals. Tellurium is far more common in the Universe as a whole than on Earth. Its extreme rarity in the Earth's crust, comparable to that of platinum, is due partly to its formation of a volatile hydride that caused tellurium to be lost to space as a gas during the hot nebular formation of Earth.

<span class="mw-page-title-main">Ytterbium</span> Chemical element, symbol Yb and atomic number 70

Ytterbium is a chemical element; it has symbol Yb and atomic number 70. It is a metal, the fourteenth and penultimate element in the lanthanide series, which is the basis of the relative stability of its +2 oxidation state. Like the other lanthanides, its most common oxidation state is +3, as in its oxide, halides, and other compounds. In aqueous solution, like compounds of other late lanthanides, soluble ytterbium compounds form complexes with nine water molecules. Because of its closed-shell electron configuration, its density, melting point and boiling point are much lower than those of most other lanthanides.

<span class="mw-page-title-main">Cubic crystal system</span> Crystallographic system where the unit cell is in the shape of a cube

In crystallography, the cubiccrystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.

Chalcogenide glass is a glass containing one or more chalcogens. Up until recently, chalcogenide glasses (ChGs) were believed to be predominantly covalently bonded materials and classified as covalent network solids. A most recent and extremely comprehensive university study of more than 265 different ChG elemental compositions, representing 40 different elemental families now shows that the vast majority of chalcogenide glasses are more accurately defined as being predominantly bonded by the weaker van der Waals forces of atomic physics and more accurately classified as van der Waals network solids. They are not exclusively bonded by these weaker vdW forces, and do exhibit varying percentages of covalency, based upon their specific chemical makeup. Polonium is also a chalcogen but is not used because of its strong radioactivity. Chalcogenide materials behave rather differently from oxides, in particular their lower band gaps contribute to very dissimilar optical and electrical properties.

<span class="mw-page-title-main">Chalcogenide</span>

A chalcogenide is a chemical compound consisting of at least one chalcogen anion and at least one more electropositive element. Although all group 16 elements of the periodic table are defined as chalcogens, the term chalcogenide is more commonly reserved for sulfides, selenides, tellurides, and polonides, rather than oxides. Many metal ores exist as chalcogenides. Photoconductive chalcogenide glasses are used in xerography. Some pigments and catalysts are also based on chalcogenides. The metal dichalcogenide MoS2 is a common solid lubricant.

<span class="mw-page-title-main">Zinc telluride</span> Chemical compound

Zinc telluride is a binary chemical compound with the formula ZnTe. This solid is a semiconductor material with a direct band gap of 2.26 eV. It is usually a p-type semiconductor. Its crystal structure is cubic, like that for sphalerite and diamond.

GeSbTe (germanium-antimony-tellurium or GST) is a phase-change material from the group of chalcogenide glasses used in rewritable optical discs and phase-change memory applications. Its recrystallization time is 20 nanoseconds, allowing bitrates of up to 35 Mbit/s to be written and direct overwrite capability up to 106 cycles. It is suitable for land-groove recording formats. It is often used in rewritable DVDs. New phase-change memories are possible using n-doped GeSbTe semiconductor. The melting point of the alloy is about 600 °C (900 K) and the crystallization temperature is between 100 and 150 °C.

<span class="mw-page-title-main">Bismuth telluride</span> Chemical compound

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.

<span class="mw-page-title-main">Tin telluride</span> Chemical compound

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.

Samarium(III) sulfide (Sm2S3) is a chemical compound of the rare earth element samarium, and sulfur. In this compound samarium is in the +3 oxidation state, and sulfur is an anion in the −2 state.

The chalcogens react with each other to form interchalcogen compounds.

<span class="mw-page-title-main">Samarium hexaboride</span> Chemical compound

Samarium hexaboride (SmB6) is an intermediate-valence compound where samarium is present both as Sm2+ and Sm3+ ions at the ratio 3:7. It is a Kondo insulator having a metallic surface state.

<span class="mw-page-title-main">Tungsten diselenide</span> Chemical compound

Tungsten diselenide is an inorganic compound with the formula WSe2. The compound adopts a hexagonal crystalline structure similar to molybdenum disulfide. The tungsten atoms are covalently bonded to six selenium ligands in a trigonal prismatic coordination sphere while each selenium is bonded to three tungsten atoms in a pyramidal geometry. The tungsten–selenium bond has a length of 0.2526 nm, and the distance between selenium atoms is 0.334 nm. It is a well studied example of a layered material. The layers stack together via van der Waals interactions. WSe2 is a very stable semiconductor in the group-VI transition metal dichalcogenides.

<span class="mw-page-title-main">Molybdenum ditelluride</span> Chemical compound

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.

<span class="mw-page-title-main">Tantalum diselenide</span> Chemical compound

Tantalum diselenide is a compound made with tantalum and selenium atoms, with chemical formula TaSe2, which belongs to the family of transition metal dichalcogenides. In contrast to molybdenum disulfide (MoS2) or rhenium disulfide (ReS2), tantalum diselenide does not occur spontaneously in nature, but it can be synthesized. Depending on the growth parameters, different types of crystal structures can be stabilized.

<span class="mw-page-title-main">Europium compounds</span> Compounds with at least one europium atom

Europium compounds are compounds formed by the lanthanide metal europium (Eu). In these compounds, europium generally exhibits the +3 oxidation state, such as EuCl3, Eu(NO3)3 and Eu(CH3COO)3. Compounds with europium in the +2 oxidation state are also known. The +2 ion of europium is the most stable divalent ion of lanthanide metals in aqueous solution. Many europium compounds fluoresce under ultraviolet light due to the excitation of electrons to higher energy levels. Lipophilic europium complexes often feature acetylacetonate-like ligands, e.g., Eufod.

Samarium compounds are compounds formed by the lanthanide metal samarium (Sm). In these compounds, samarium generally exhibits the +3 oxidation state, such as SmCl3, Sm(NO3)3 and Sm(C2O4)3. Compounds with samarium in the +2 oxidation state are also known, for example SmI2.

References

  1. 1 2 3 4 Jayaraman, A.; Narayanamurti, V.; Bucher, E.; Maines, R. (1970). "Continuous and Discontinuous Semiconductor-Metal Transition in Samarium Monochalcogenides Under Pressure". Physical Review Letters. 25 (20): 1430. Bibcode:1970PhRvL..25.1430J. doi:10.1103/PhysRevLett.25.1430.
  2. 1 2 Kitagawa, R.; Takebe, H.; Morinaga, K. (2003). "Photoinduced phase transition of metallic SmS thin films by a femtosecond laser". Applied Physics Letters. 82 (21): 3641. Bibcode:2003ApPhL..82.3641K. doi:10.1063/1.1577824.
  3. 1 2 3 Rogers, E; Smet, P F; Dorenbos, P; Poelman, D; Van Der Kolk, E (2010). "The thermally induced metal–semiconducting phase transition of samarium monosulfide (SmS) thin films" (free download). Journal of Physics: Condensed Matter. 22 (1): 015005. Bibcode:2010JPCM...22a5005R. doi:10.1088/0953-8984/22/1/015005. PMID   21386220. S2CID   17888041.
  4. 1 2 K. H. J. Buschow Concise encyclopedia of magnetic and superconducting materials, Elsevier, 2005 ISBN   0-08-044586-1 p. 318
  5. ↑ Emsley, John (2001). "Samarium". Nature's Building Blocks: An A-Z Guide to the Elements. Oxford, England, UK: Oxford University Press. p.  374. ISBN   978-0-19-850340-8.
  6. 1 2 Eric Beaurepaire (Ed.) Magnetism: a synchrotron radiation approach, Springer, 2006 ISBN   3-540-33241-3 p. 393
  7. ↑ De Tomasi, F (2002). "Laser irradiation effects on the resistance of SmS films". Thin Solid Films. 413 (1–2): 171–176. Bibcode:2002TSF...413..171D. doi:10.1016/S0040-6090(02)00235-3.
  8. ↑ Elmegreen, Bruce G. et al. Piezo-driven non-volatile memory cell with hysteretic resistance US patent application 12/234100, 09/19/2008
  9. ↑ SmS Tenzo Archived 2012-03-15 at the Wayback Machine
  10. ↑ Kaminskii, V. V.; Solov’ev, S. M.; Golubkov, A. V. (2002). "Electromotive Force Generation in Homogeneously Heated Semiconducting Samarium Monosulfide". Technical Physics Letters. 28 (3): 229. Bibcode:2002TePhL..28..229K. doi:10.1134/1.1467284. S2CID   122463906. Archived from the original on 2012-03-15. other articles on this topic Archived 2012-03-15 at the Wayback Machine
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