Langbeinites Explained

Langbeinites are a family of crystalline substances based on the structure of langbeinite with general formula, where M is a large univalent cation (such as potassium, rubidium, caesium, or ammonium), and M' is a small divalent cation (for example, magnesium, calcium, manganese, iron, cobalt, nickel, copper, zinc or cadmium). The sulfate group,, can be substituted by other tetrahedral anions with a double negative charge such as tetrafluoroberyllate, selenate, chromate, molybdate, or tungstates. Although monofluorophosphates are predicted, they have not been described. By redistributing charges other anions with the same shape such as phosphate also form langbeinite structures. In these the M' atom must have a greater charge to balance the extra three negative charges.

At higher temperatures the crystal structure is cubic P213. However, the crystal structure may change to lower symmetries at lower temperatures, for example, P21, P1, or P212121. Usually this temperature is well below room temperature, but in a few cases the substance must be heated to acquire the cubic structure.

Crystal structure

The crystal structures of langbeinites consist of a network of oxygen vertex-connected tetrahedral polyanions (such as sulfate) and distorted metal ion-oxygen octahedra. The unit cell contains four formula units. In the cubic form the tetrahedral anions are slightly rotated from the main crystal axes. When cooled, this rotation disappears and the tetrahedra align, resulting in lower energy as well as lower crystal symmetry.

Examples

Sulfates include dithallium dicadmium sulfate,[1] dirubidium dicadmium sulfate,[2] dipotassium dicadmium sulfate,[3] dithallium manganese sulfate,[4] and dirubidium dicalcium trisulfate.[5]

Selenates include diammonium dimanganese selenate. A diammonium dicadmium selenate langbeinite could not be crystallised from water, but a trihydrate exists.[6]

Chromate based langbeinites include dicaesium dimanganese chromate.

Molybdates include . Potassium members are absent, as are zinc and copper containing solids, which all crystallize in different forms. Manganese, magnesium, cadmium and some nickel double molybdates exist as langbeinites.[7]

Double tungstates of the form are predicted to exist in the langbeinite form.

An examples with tetrafluroberyllate is dipotassium dimanganese tetrafluoroberyllate .[8] Other tetrafluoroberyllates may include: ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ;.[9]

The phosphate containing langbeinites were found in 1972 with the discovery of, and since then a few more phosphates that also contain titanium have been found such as and . By substituting metals in, A from (K, Rb, Cs), and M from (Cr, Fe, V), other langbeinites are made. The NASICON-type structure competes for these kinds of phosphates, so not all possibilities are langbeinites.Other phosphate based substances include,,,,[10],[11] .[12] Sodium barium diiron tris-(phosphate) is yet another variation with the same structure but differently charged ions.[13] Most phosphates of this kind of formula do not form langbeinites, instead crystallise in the NASICON structure with archetype .[10]

A langbeinite with arsenate is known to exist by way of .[14]

Properties

Physical properties

Langbeinite-family crystals can show ferroelectric or ferroelastic properties.[10] Diammonium dicadmium sulfate identified by Jona and Pepinsky[15] with a unit cell size of 10.35 Å becomes ferroelectric when the temperature drops below 95 K.[16] The phase transition temperature is not fixed, and can vary depending on the crystal or history of temperature change. So for example the phase transition in diammonium dicadmium sulfate can occur between 89 and 95 K.[17] Under pressure the highest phase transition temperature increases. ∂T/∂P = 0.0035 degrees/bar. At 824 bars there is a triple point with yet another transition diverging at a slope of ∂T/∂P = 0.103 degrees/bar.[18] For dipotassium dimanganese sulfate pressure causes the transition to rise at the rate of 6.86 °C/kbar. The latent heat of the transition is 456 cal/mol.[19]

Dithallium dicadmium sulfate was shown to be ferroelectric in 1972.[20]

Dipotassium dicadmium sulfate is thermoluminescent with stronger outputs of light at 350 and 475 K. This light output can be boosted forty times with a trace amount of samarium.[21] Dipotassium dimagnesium sulfate doped with dysprosium develops thermoluminescence and mechanoluminescence after being irradiated with gamma rays.[22]

Notes and References

  1. Guelylah . A. . G. Madariaga . W. Morgenroth . M. I. Aroyo . T. Breczewski . E. H. Bocanegra . 2000 . X-ray structure determination of the monoclinic (121 K) and orthorhombic (85 K) phases of langbeinite-type dithallium dicadmium sulfate . Acta Crystallographica Section B . 56 . 6 . 921–935 . 10.1107/S0108768100009514 . 11099956. 2000AcCrB..56..921G .
  2. Guelylah . Abderrahim . Gotzon Madariaga . 2003 . Dirubidium dicadmium sulfate at 293 K. Acta Crystallographica Section C . 59 . 5 . i32–i34 . 10.1107/S0108270103007479 . 12743381. 2003AcCrC..59I..32G .
  3. Guelylah . A. . M. I. Aroyo . J. M. Pérez-Mato . 1996 . Microscopic distortion and order parameter in langbeinite K2Cd2(SO4)3 . Phase Transitions . 59 . 1–3 . 155–179 . 10.1080/01411599608220042. 1996PhaTr..59..155G .
  4. Zemann . Anna . J. Zemann . 1957 . Die Kristallstruktur von Langbeinit, K2Mg2(SO4)3 . Acta Crystallographica . 10 . 6 . 409–413 . 10.1107/S0365110X57001346. free . 1957AcCry..10..409Z .
  5. Boujelben . Mohamed . Mohamed Toumi . Tahar Mhiri . 2007 . Langbeinite-type Rb2Ca2(SO4)3 . Acta Crystallographica Section E . 63 . 7 . i157 . 10.1107/S1600536807027043. 2007AcCrE..63I.157B .
  6. Martínez . M. L. . Rodriguez . A. . Mestres . L. . Solans . X. . Bocanegra . E. H. . Synthesis, crystal structure, and thermal studies of (NH4)2Cd2(SeO4)3·3H2O . Journal of Solid State Chemistry . November 1990 . 89 . 1 . 88–93 . 10.1016/0022-4596(90)90297-B . 1990JSSCh..89...88M .
  7. Солодовникова . С. Ф. . Солодовникова, В. А. . 1997 . Новый тип строения в морфотропном ряду A+2M+2(MoO4)3: кристаллическая структура Rb2Cu2(MoO4)3 . ЖУРНАЛ структур. химии . 38 . 5 . 914–921 . Russian .
  8. Guelylah . A. . T. Breczewski . G. Madariaga . 1996 . A New Langbeinite: Dipotassium Dimanganese Tetrafluoroberyllate . Acta Crystallographica Section C . 52 . 12 . 2951–2954 . 10.1107/S0108270196008827. 1996AcCrC..52.2951G .
  9. Book: Pies, W. . A. Weiss . 1973 . 7a . 91–103 . 10.1007/10201462_9 . A458, I.1.3 Complex fluorides and fluorine double salts . Key Elements: F, Cl, Br, I . Landolt-Börnstein - Group III Condensed Matter . 978-3-540-06166-3.
  10. Norberg . Stefan T. . 2002 . New phosphate langbeinites, K2MTi(PO4)3 (M = Er, Yb or Y), and an alternative description of the langbeinite framework . Acta Crystallographica B . 58 . 5 . 743–749 . 12324686 . 10.1107/S0108768102013782 . 2391006. 2002AcCrB..58..743N .
  11. Li . Hai-Yan . Dan Zhao . 2011 . A new langbeinite-type phosphate: K2AlSn(PO4)3 . Acta Crystallographica Section E . 67 . 10 . i56 . 10.1107/S1600536811037263 . 22058680. 3201338. 2011AcCrE..67I..56L .
  12. Gustafsson . Joacim C. M. . Stefan T. Norberg . Göran Svensson . 2006 . The langbeinite type Rb2TiY(PO4)3 . Acta Crystallographica Section E . 62 . 7 . i160–i162 . 10.1107/S1600536806021635. 2006AcCrE..62I.160G .
  13. Hidouri . Mourad . Hasna Jerbi . Mongi Ben Amara . 2008 . The iron phosphate NaBaFe2(PO4)3 . Acta Crystallographica Section E . 64 . 8 . i51 . 10.1107/S1600536808023040 . 21202994 . 2961906. 2008AcCrE..64I..51H .
  14. Harrison . William T. A. . 2010 . K2ScSn(AsO4)3: an arsenate-containing langbeinite . Acta Crystallographica Section C . 66 . 7 . i82–i84 . 10.1107/S0108270110021670 . 20603547 . 2010AcCrC..66I..82H .
  15. Jona . F. . R. Pepinsky . 1956 . Ferroelectricity in the Langbeinite System . Physical Review . 103 . 4 . 1126 . 10.1103/PhysRev.103.1126 . 1956PhRv..103.1126J.
  16. McDowell . C. A. . P. Raghunathan . R. Srinivasan . 1975 . Proton N.M.R. study of the dynamics of the ammonium ion in ferroelectric langbeinite, (NH4)2Cd2(SO4)3 . Molecular Physics . 29 . 3 . 815–824 . 10.1080/00268977500100721 . 1975MolPh..29..815M.
  17. Web site: Structural Study of Langbeinite-type ((NH4)2Cd2(SO4)3) Crystal in the High Temperature Phase . Moriyoshi . C. . E. Magome . K. Itoh . 28 March 2007 . IMF-11 . 24 June 2013.
  18. Glogarová . M. . C. Frenzel . E. Hegenbarth . 1972 . The Behaviour of (NH4)2Cd2(SO4)3 under Pressure . Physica Status Solidi B . 53 . 1 . 369–372 . 10.1002/pssb.2220530139 . 1972PSSBR..53..369G.
  19. Hikita . Tomoyuki . Makoto Kitabatake . Takuro Ikeda . 1979 . Hydrostatic Pressure Effect on the Phase Transition of K2Mn2(SO4)3 . Journal of the Physical Society of Japan . 46 . 2 . 695–696 . 10.1143/JPSJ.46.695 . 1979JPSJ...46..695H.
  20. Brzina . B. . M. Glogarová . 1972 . New ferroelectric langbeinite Tl2Cd2(SO4)3 . Physica Status Solidi A . 11 . 1 . K39–K42 . 10.1002/pssa.2210110149 . 1972PSSAR..11...39..
  21. Deshmukh . B. T. . S. V. Bodade . S. V. Moharil . 1986 . Thermoluminescence of K2Cd2(SO4)3 . Physica Status Solidi A . 98 . 1 . 239–246 . 10.1002/pssa.2210980127 . 1986PSSAR..98..239D.
  22. Panigrahi . A. K. . Dhoble, S. J. . Kher, R. S. . Moharil, S. V. . 2003 . Thermo and mechanoluminescence of Dy3+ activated .

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