Amorphous State

Chapter

Abstract

Below certain grain size, estimated from X-ray diffraction or thermodynamic calculations as 1 to 5 nm, a crystal loses its long-range order due to increased fraction of surface atoms with incomplete and distorted coordination. If a sharp freezing or a chemical reaction under shock compression precludes the growth of bigger particles, an amorphous solid (glass) will result. The structural chemistry of melting is discussed in terms of average bond distances and effective coordination numbers. For binary compounds and metals, these usually decrease on melting, but for low-coordinate non-metals tend to increase. The structural science of liquid water and aqueous solutions is briefly reviewed, from the Bernal–Fowler model (1933) to the recent computer simulations and extreme-conditions experiments on dynamic ionization. In diluted solutions of salts, ions replace water molecules and are 4-coordinate, while in concentrated solutions ions coordinate water molecules around them in structures similar to solid hydrates.

Keywords

Coordination Number Shock Compression Crystalline Hydrate Solvation Sphere Pure Ammonia 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

References

  1. 1.
    Roy R (1970) Classification of non-crystalline solids. J Non-Cryst Solids 3:33–40Google Scholar
  2. 2.
    Stace AJ (2002) Metal ion solvation in the gas phase: the quest for higher oxidation states. J Phys Chem A 106:7993–6005Google Scholar
  3. 3.
    Batsanov SS, Bokarev VP (1980) The limit of crushing of inorganic substances. Inorg Mater 16:1131–1133Google Scholar
  4. 4.
    Palosz B, Grzanka E, Gierlotka S et al (2002) Analysis of short and long range atomic order in nanocrystalline diamonds with application of powder diffractometry. Z Krist 217:497–509Google Scholar
  5. 5.
    Rempel A, Magerl A (2010) Non-periodicity in nanoparticles with close-packed structures. Acta Cryst A 66:479–483Google Scholar
  6. 6.
    Bokarev VP (1986) Geometric estimate of the atomic coordination numbers in defect crystals of inorganic substances. Inorg Mater 22:306–307Google Scholar
  7. 7.
    Batsanov SS (2008) Experimental foundations of structural chemistry. Moscow Univ Press, MoscowGoogle Scholar
  8. 8.
    Pirkkalainen K, Serimaa R (2009) Non-periodicity in nanoparticles with close-packed structures. J Appl Cryst 42:442–447Google Scholar
  9. 9.
    Seyller Th, Diehl RD, Jona F (1999) Low-energy electron diffraction study of the multilayer relaxation of Cu(211). J Vacuum Sci Techn A 17:1635–1638Google Scholar
  10. 10.
    Parkin SR, Watson PR, McFarlane RA, Mitchell KAR (1991) A revised LEED determination of the relaxations present at the (311) surface of copper. Solid State Commun 78:841–843Google Scholar
  11. 11.
    Tian Y, Quinn J, Lin K-W, Jona F (2000) Cu{320} Structure of stepped surfaces. Phys Rev B 61:4904–4909Google Scholar
  12. 12.
    Nascimento VB, Soares EA, de Carvalho VE et al (2003) Thermal expansion of the Ag(110) surface studied by low-energy electron diffraction and density-functional theory. Phys Rev B 68:245408Google Scholar
  13. 13.
    Davis HL, Hannon JB, Ray KB, Plummer FW (1992) Anomalous interplanar expansion at the (0001) surface of Be. Phys Rev Lett 68:2632–2635PubMedGoogle Scholar
  14. 14.
    Li YS, Quinn J, Jonna F, Marcus PM (1989) Low-energy electron diffraction study of multilayer relaxation on a Pb{110} surface. Phys Rev B 40:8239–8244Google Scholar
  15. 15.
    Lin RF, Li YS, Jonna F, Marcus PM (1990) Low-energy electron diffraction study of multilayer relaxation on a Pb{001} surface. Phys Rev B 42:1150–1155Google Scholar
  16. 16.
    Li YS, Jonna F, Marcus PM (1991) Multilayer relaxation of a Pb{111} surface. Phys Rev B 43:6337–6341Google Scholar
  17. 17.
    Teeter G, Erskine JL (1999) Studies of clean metal surface relaxation experiment-theory discrepancies. Surf Rev Lett 6:813–817Google Scholar
  18. 18.
    Geng WT, Kim M, Freeman AJ (2001) Multilayer relaxation and magnetism of a high-index transition metal surface: Fe(310). Phys Rev B 63:245401Google Scholar
  19. 19.
    Over H, Kleinle G, Ertl G et al (1991) A LEED structural analysis of the Co(10\(\overline 1 \)0) surface. Surf Sci 254:L469–L474Google Scholar
  20. 20.
    Geng WT, Freeman AJ, Wu RQ (2001) Magnetism at high-index transition-metal surfaces and the effect of metalloid impurities: Ni (210). Phys Rev B 63:064427Google Scholar
  21. 21.
    Zhang X-G, Van Hove MA, Somorjai GA et al (1991) Efficient determination of multilayer relaxation in the Pt(210) stepped and densely kinked surface. Phys Rev Lett 67:1298–1301PubMedGoogle Scholar
  22. 22.
    Härtel S, Vogt J, Weiss H (2010) Relaxation and thermal vibrations at the NaF(100) surface. Surf Sci 604:1996–2001Google Scholar
  23. 23.
    Vogt J (2007) Tensor LEED study of the temperature dependent dynamics of the NaCl(100) single crystal surface. Phys Rev B 75:125423Google Scholar
  24. 24.
    Okazawa T, Nishimura T, Kido Y (2002) Surface structure and lattice dynamics of KI(001) studied by high-resolution ion scattering combined with molecular dynamics simulation. Phys Rev B 66:125402Google Scholar
  25. 25.
    Palosz B, Pantea C, Grazanka E et al (2006) Investigation of relaxation of nanodiamond surface in real and reciprocal spaces. Diamond Relat Mater 15:1813–1817Google Scholar
  26. 26.
    Sun CQ, Tay BK, Zeng XT et al (2002) Bond-order–bond-length–bond-strength (bond-OLS) correlation mechanism for the shape-and-size dependence of a nanosolid. J Phys Cond Matter 14:7781–7796Google Scholar
  27. 27.
    Sun CQ (2007) Size dependence of nanostructures: impact of bond order deficiency. Prog Solid State Chem 35:1–159Google Scholar
  28. 28.
    Feibelman PJ (1996) Relaxation of hcp(0001) surfaces: a chemical view. Phys Rev B 53:13740–13746Google Scholar
  29. 29.
    Batsanov SS (1987) Effect of high dynamic pressure on the structure of solids. Propellants Explosives Pyrotechnics 12:206–208Google Scholar
  30. 30.
    Batsanov SS (1994) Effects of explosions on materials. Springer-Verlag, New YorkGoogle Scholar
  31. 31.
    Batsanov SS, Bоkаrеv VP, Моrоz IK (1982) Solid solution in the KCl-CsCl system. Russ J Inorg Chem 26:1557–1559Google Scholar
  32. 32.
    Kinugawa K, Othori N, Kadono K et al (1993) Pulsed neutron diffraction study on the structures of glassy LiX–KX–CsX–BaX2 (X=Cl, Br, I). J Chem Phys 99:5345–5351Google Scholar
  33. 33.
    Noda Y, Nakao H, Terauchi H (1995) Neutron incoherent scattering of structural glass NH4I–KI mixed crystal. Physica B 213–214:564–566Google Scholar
  34. 34.
    Micoulaut M, Cormier L, Henderson GS (2006) The structure of amorphous, crystalline and liquid GeO2. J Phys Conden Matter 18:R753–R784Google Scholar
  35. 35.
    Delaplane RG, Dahlborg U, Howells WS, Lundström T (1988) A neutron diffraction study of amorphous boron. J Non-Cryst Solids 106:66–69Google Scholar
  36. 36.
    Degtyareva VF, Degtyareva O, Mao H-K, Hemley RJ (2006) High-pressure behavior of CdSb: compound decomposition, phase formation, and amorphization. Phys Rev B 73:214108Google Scholar
  37. 37.
    Marks NA, McKenzie DR, Pailthorpe BA et al (1996) Microscopic structure of tetrahedral amorphous carbon. Phys Rev Lett 76:768–771PubMedGoogle Scholar
  38. 38.
    Sinclair RN, Stone CE, Wright AC et al (2001) The structure of vitreous boron sulphide. J Non-Cryst Solids 293–295:383–388Google Scholar
  39. 39.
    Yao W, Martin SW, Petkov V (2005) Structure determination of low-alkali-content Na2S + B2S3 glasses using neutron and synchrotron X-ray diffraction. J Non-Cryst Solids 351:1995–2002Google Scholar
  40. 40.
    Boswell FWC (1951) Precise determination of lattice constants by electron diffraction and variations in the lattice constants of very small crystallites. Proc Phys Soc London A 64:465–475Google Scholar
  41. 41.
    Yamanaka T, Sugiyama K, Ogata K (1992) Kinetic study of the GeO2 transition under high pressures using synchrotron X-radiation. J Appl Cryst 25:11–15Google Scholar
  42. 42.
    Batsanov SS, Bokarev VP (1987) Existence of polymorphic modifications in the amorphous state. Inorg Mater 23:946–947Google Scholar
  43. 43.
    Hoppe U, Walter G, Barz A et al (1998) The P-O bond lengths in vitreous P2O5 probed by neutron diffraction with high real-space resolution. J Phys Cond Matter 10:261–270Google Scholar
  44. 44.
    Brazhkin VV, Gavrilyuk AG, Lyapin AG et al (2007) AsS: bulk inorganic molecular-based chalcogenide glass. Appl Phys Lett 91:031912Google Scholar
  45. 45.
    Kajihara Y, Inui M, Matsuda K et al (2007) X-ray diffraction measurement of liquid As2Se3 by using third-generation synchrotron radiation. J Non-Cryst Solids 353:1985–1989Google Scholar
  46. 46.
    Dongo M, Gerber Th, Hafiz M et al (2006) On the structure of As2Te3 glass. J Phys Cond Matter 18:6213–6224Google Scholar
  47. 47.
    Tanaka K (1988) Layer structures in chalcogenide glasses. J Non-Cryst Solids 103:149–150Google Scholar
  48. 48.
    Tanaka K (1989) Structural phase transitions in chalcogenide glasses. Phys Rev B 39:1270–1279Google Scholar
  49. 49.
    Suzuki M, Okazaki H (1977) The structure of α-AgI. Phys Stat Solidi 42a:133–140Google Scholar
  50. 50.
    Keen DA, Hayes W, McGreevy RL (1990) Structural disorder in AgBr on the approach to melting. J Phys Cond Matter 2:2773–2786Google Scholar
  51. 51.
    Ubbelodе АR (1978) The molted state of matter. Wiley, New YorkGoogle Scholar
  52. 52.
    Tosi MP (1994) Structure of covalent liquids. J Phys Cond Matter 6:A13–A28Google Scholar
  53. 53.
    Waseda Y, Tamaki S (1975) Structural study of Pt and Cr in the liquid state by X-ray diffraction. High Temp-High Press 7:215–220Google Scholar
  54. 54.
    Waseda Y (1980). The structure of non-crystalline materials: liquids and amorphous solids. McGraw Hill, New York.Google Scholar
  55. 55.
    Vahvaselkä KS (1978) X-ray diffraction analysis of liquid Hg, Sn, Zn, Al and Cu. Phys Scripta 18:266–274Google Scholar
  56. 56.
    Krishnan S, Ansell S, Feleten JJ et al (1998) Structure of liquid boron. Phys Rev Lett 81:586–589Google Scholar
  57. 57.
    Anselm A, Krishnan Sh, Felten JJ, Price DL (1998) Structure of supercooled liquid silicon. J Phys Cond Matter 10:L73–L78Google Scholar
  58. 58.
    Di Cicco A, Aquilanti G, Minicucci M et al (1999) Short-range interaction in liquid rhodium probed by x-ray absorption spectroscopy. J Phys Cond Matter 11:L43–L50Google Scholar
  59. 59.
    Wei S, Oyanagi H, Liu W et al (2000) Local structure of liquid gallium studied by X-ray absorption fine structure. J Non-Cryst Solids 275:160–168Google Scholar
  60. 60.
    Katayama Y, Mizutani T, Utsumi W et al (2000) A first-order liquid–liquid phase transition in phosphorus. Nature 403:170–173PubMedGoogle Scholar
  61. 61.
    Holland-Moritz D, Schenk T, Bellisent R et al (2002) Short-range order in undercooled Co melts. J Non-Cryst Solids 312–314:47–51Google Scholar
  62. 62.
    Schenk T, Holland-Moritz D, Simonet V et al (2002) Icosahedral short-range order in deeply undercooled metallic melts. Phys Rev Lett 89:075507PubMedGoogle Scholar
  63. 63.
    Jakse N, Hennet L, Price DL et al (2003) Structural changes on supercooling liquid silicon. Appl Phys Lett 83:4734–4736Google Scholar
  64. 64.
    Salmon PS, Petri I, de Jong PHK et al (2004) Structure of liquid lithium. J Phys Cond Matter 16:195–222Google Scholar
  65. 65.
    Wasse JC, Salmon PS (1999) Structure of molten lanthanum and cerium tri-halides by the method of isomorphic substitution in neutron diffraction. J Phys Cond Matter 11:1381–1396Google Scholar
  66. 66.
    Iwadate, Suzuki, K, Onda, N et al (2006) Structural changes on supercooling liquid silicon. J Alloys Compd 408–412:248–252Google Scholar
  67. 67.
    Ensico E, Lombardero M, Dore JC (1986) A RISM analysis of neutron diffraction data for SiCl4/TiCl4 and SnCl4/TiCl4 liquid mixtures. Mol Phys 59:941–952Google Scholar
  68. 68.
    Funamori N, Tsuji K (2002) Pressure-induced structural change of liquid silicon. Phys Rev Lett 88:255508Google Scholar
  69. 69.
    Cahoon JR (2004) The first coordination number for liquid metal. Canad J Phys 82:291–301Google Scholar
  70. 70.
    Santiso E, Müller EA (2002) Dense packing of binary and polydisperse hard spheres. Mol Phys 100:2461–2469Google Scholar
  71. 71.
    Katayama Y, Tsuji K (2003) X-ray structural studies on elemental liquids under high pressures. J Phys Cond Matter 15:6085–6104Google Scholar
  72. 72.
    Sanloup C, Guyot F, Gillet P et al (2000) Structural changes in liquid Fe at high pressures and high temperatures from Synchrotron X-ray diffraction. Europhys Lett 52:151–157Google Scholar
  73. 73.
    Shen G, Sata N, Taberlet N et al (2002) Melting studies of indium: determination of the structure and density of melts at high pressures and high temperatures. J Phys Cond Matter 14:10533–10540Google Scholar
  74. 74.
    Takeda S, Tamaki S, Waseda Y (1985) Electron-ion correlation in liquid metals. J Phys Soc Japan 54:2552–2258Google Scholar
  75. 75.
    Takeda S, Tamaki S, Waseda Y, Harada S (1986) Electron’s distribution in liquid zinc and lead. J Phys Soc Japan 55:184–192Google Scholar
  76. 76.
    Takeda S, Harada S, Tamaki S, Waseda Y (1988) Electron charge distribution in liquid metals. Z phys Chem NF 157:459–463Google Scholar
  77. 77.
    Takeda S, Inui M, Tamaki S et al (1993) Electron charge distribution in liquid Te. J Phys Soc Japan 62:4277–4286Google Scholar
  78. 78.
    Takeda S, Inui M, Tamaki S et al (1994) Electron-ion correlation in liquid magnesium. J Phys Soc Japan 63:1794–1802Google Scholar
  79. 79.
    Tao DP (2005) Prediction of the coordination numbers of liquid metals. Metallurg Mater Trans A 36:3495–3497Google Scholar
  80. 80.
    Regan MJ, Kawamoto EH, Lee S et al (1995) Surface layering in liquid gallium: an X-ray reflectivity study. Phys Rev Lett 75:2498–2501PubMedGoogle Scholar
  81. 81.
    Tostmann H, DiMasi E, Pershan PS et al (1999) X-ray studies on liquid indium:Surface structure of liquid metals and the effect of capillary waves. Phys Rev B 59:783–791Google Scholar
  82. 82.
    Shpyrko OG, Grigoriev AY, Steimer Ch et al (2004) Anomalous layering at the liquid Sn surface. Phys Rev B 70:224206Google Scholar
  83. 83.
    Magnussen OM, Ocko BM, Regan MJ et al (1995) X-ray reflectivity measurements of surface layering in liquid mercury. Phys Rev Lett 75:4444–4447Google Scholar
  84. 84.
    Shpyrko O, Fukuto M, Pershan P et al (2004) Surface layering of liquids: the role of surface tension. Phys Rev B 69:245423Google Scholar
  85. 85.
    Stolz M, Winter R, Howells WS (1994) The structural properties of liquid and quenched sulphur II. J Phys Cond Matter 6:3619–3628Google Scholar
  86. 86.
    Raty J-Y, Gaspard J-P, Bionducci N et al (1999) On the structure of liquid IV–VI semiconductors. J Non-Cryst Solids 250–252:277–280Google Scholar
  87. 87.
    Thomas JM (2004) Ultrafast electron crystallography: the dawn of a new era. Angew Chem Int Ed 43:2606–2610Google Scholar
  88. 88.
    Sokolowski-Tinten K, Blome C, Dietrich C et al (2001) Femtosecond X-ray measurement of ultrafast melting and large acoustic transients. Phys Rev Lett 87:225701PubMedGoogle Scholar
  89. 89.
    Rousse A, Rischel C, Fourmaux S et al (2001) Non-thermal melting in semiconductors measured at femtosecond resolution. Nature 410:65–68PubMedGoogle Scholar
  90. 90.
    Sаmоylоv ОYa (1957) Structure of water solutions of electrolytes and hydration of ionics. Academy of Science of the USSR, Мoscow (in Russian)Google Scholar
  91. 91.
    Bernal JD, Fowler RH (1933) A theory of water and ionic solution. J Chem Phys 1:515–548Google Scholar
  92. 92.
    Hattori T, Taga N, Takasugi Y et al (2002) Structure of liquid GaSb under pressure. J Non-Cryst Solids 312–314:26–29Google Scholar
  93. 93.
    Malenkov GG (2006) Sructure and dynamics of liquid water. J Struct Chem 47:S1–S31Google Scholar
  94. 94.
    Goncharov AF, Goldman N, Fried LE et al (2005) Dynamic ionization of water under extreme conditions. Phys Rev Lett 94:125508PubMedGoogle Scholar
  95. 95.
    Markus Y (1988) Ionic radii in aqueous solutions. Chem Rev 88:1475–1498Google Scholar
  96. 96.
    Johansson G (1992) Structures of complexes in solution derived from X-ray diffraction measurements. Adv Inorg Chem 39:159–232Google Scholar
  97. 97.
    Ohtaki H, Radnai T (1993) Structure and dynamics of hydrated ions. Chem Rev 93:1157–1204Google Scholar
  98. 98.
    Blixt J, Glaster J, Mink J et al (1995) Structure of thallium(III) chloride, bromide, and cyanide complexes in aqueous solution. J Am Chem Soc 117:5089–5104Google Scholar
  99. 99.
    D’Angelo P, Bottari E, Festa MR et a (1997) Structural investigation of copper(II) chloride solutions using X-ray absorption spectroscopy. J Chem Phys 107:2807–2812Google Scholar
  100. 100.
    Ramos S, Neilson GW, Barnes AC, Buchanan P (2005) An anomalous x-ray diffraction study of the hydration structures of Cs+ and I in concentrated solutions. J Chem Phys 123:214501PubMedGoogle Scholar
  101. 101.
    Hofer TS, Randolf BR, Rode BM, Persson I (2009) The hydrated platinum (II) ion in aqueous solution—a combined theoretical and EXAFS spectroscopic study. Dalton Trans 1512–1515Google Scholar
  102. 102.
    Persson I (2010) Hydrated metal ions in aqueous solution: how regular are their structures? Pure Appl Chem 82:1901–1917Google Scholar
  103. 103.
    Mähler J, Persson I (2012) A study of the hydration of the alkali metal ions in aqueous solution. Inorg Chem 51:425−438PubMedGoogle Scholar
  104. 104.
    Näslund L-Å, Edwards DC, Wernet P et al (2005) X-ray absorption spectroscopy study of the hydrogen bond network in the bulk water of aqueous solutions. J Phys Chem A 109:5995–6002PubMedGoogle Scholar
  105. 105.
    Drаkin SI (1963) Me−H2O distances in crystal hydrates and radii of ions in aqueous solution. J Struct Chem 4:472–478Google Scholar
  106. 106.
    Friedman HL, Lewis L (1976) The coordination geometry of water in some salt hydrates. J Solution Chem 5:445–455Google Scholar
  107. 107.
    Persson I, Sandström M, Yokoyama H, Chaudhry M (1995) Structure of the solvated strontium and barium ions in aqueous, dimethyl-sulfoxide and pyridine solution, and crystal-structure of strontium and barium hydroxide octahydrate. Z Naturforsch 50:21–37Google Scholar
  108. 108.
    Schmid R, Miah AM, Sapunov VN (2000) A new table of the thermodynamic quantities of ionic hydration: values and some applications (enthalpy-entropy compensation and Born radii). Phys Chem Chem Phys 2:97–102Google Scholar
  109. 109.
    Torapava N, Persson I, Eriksson L, Lundberg D (2009) Hydration and hydrolysis of thorium(IV) in aqueous solution and the structures of two crystalline thorium(IV) hydrates. Inorg Chem 48:11712–11723PubMedGoogle Scholar
  110. 110.
    Inada Y, Sugimoto K, Ozutsumi K, Funahashi S (1994) Solvation structures of manganese(II), iron(II), cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), and indium(III) ions in 1,1,3,3-tetramethylurea as studied by EXAFS and electronic spectroscopy. Variation of coordination number. Inorg Chem 33:1875–1880Google Scholar
  111. 111.
    Ulvenlund S, Wheatley A, Bengtsson L (1995) Spectroscopic investigation of concentrated solutions of gallium(III) chloride in mesitylene and benzene. Dalton Trans 255–263Google Scholar
  112. 112.
    Inada Y, Hayashi H, Sugimoto K-I, Funahashi S (1999) Solvation structures of manganese(II), iron(II), cobalt(II), nickel(II), copper(II), zinc(II), and gallium(III) ions in methanol, ethanol, dimethyl sulfoxide, and trimethyl phosphate as studied by EXAFS and electronic spectroscopy. J Phys Chem A 103:1401–1406Google Scholar
  113. 113.
    Lundberg D, Ullström A-S, D’Angelo P, Persson I (2007) A structural study of the hydrated and the dimethylsulfoxide, N, N′-dimethylpropyleneurea, and N, N-dimethylthioformamide solvated iron(II) and iron(III) ions in solution and solid state. Inorg Chim Acta 360:1809–1818Google Scholar
  114. 114.
    Thompson H, Wasse JC, Skipper NT et al (2003) Structural studies of ammonia and metallic lithium–ammonia solutions. J Am Chem Soc 125:2572–2581PubMedGoogle Scholar
  115. 115.
    Hayama S, Skipper NT, Wasse JC, Thompson H (2002) X-ray diffraction studies of solutions of lithium in ammonia: the structure of the metal–nonmetal transition. J Chem Phys 116:2991–2996Google Scholar
  116. 116.
    Jacobs H, Barlage H, Friedriszik M (2004) Vergleich der kristallstrukturen der tetraammoniakate von lithiumhalogeniden, LiBr·4NH3 und LiI·4NH3, mit der struktur von tetramethylammoniumiodid, N(CH3)4I. Z anorg allgem Chem 630:645–648Google Scholar
  117. 117.
    Wasse JC, Hayama S, Skipper NT et al (2000) The structure of saturated lithium- and potassium-ammonia solutions as studied by neutron diffraction. J Chem Phys 112:7147–7151Google Scholar
  118. 118.
    Wasse JC, Howard CA, Thompson H et al (2004) The structure of calcium–ammonia solutions by neutron diffraction. J Chem Phys 121:996–1004PubMedGoogle Scholar
  119. 119.
    Tokushima T, Harada Y, Takahashi O et al (2008) High resolution X-ray emission spectroscopy of liquid water: the observation of two structural motifs. Chem Phys Lett 460:387–400Google Scholar
  120. 120.
    Röntgen WC (1892) Über die Konstitution des flüssigen Wassers. Ann Phys Chem 45:91Google Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2012

Authors and Affiliations

  1. 1.Institute of Structural Macrokinetics and Materials ScienceRussian Academy of SciencesChernogolovkaRussia
  2. 2.Chemistry DepartmentDurham UniversityDurhamUK

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