rhombohedral boron γ orthorhombic boron α tetragonal boron β tetragonal boron

Rhombohedral boron γ orthorhombic boron α

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-rhombohedral boron γ -orthorhombic boron α -tetragonal boron β -tetragonal boron High-pressure superconducting phase
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~ Page 8 of 79 ~ Silicon Amorphous silicon crystalline silicon, Diamond cubic structure Arsenic Yellow arsenic molecular non-metallic As 4 , with the same structure as white phopshorus Gray arsenic, polymeric As (metalloid) Black arsenic molecular and non-metallic, with the same structure as red phosphorus Germanium α -germanium semimetallic, with the same structure as diamond β -germanium metallic, with the same structure as beta-tin Antimony blue-white antimony stable form (metalloid), with the same structure as gray arsenic yellow antimony (non-metallic) black antimony (non-metallic) explosive antimony Tellurium amorphous tellurium - gray-black or brown powder [5] crystalline tellurium - hexagonal crystalline structure (metalloid) Metals Among the metallic elements that occur in nature in significant quantities (56 up to U, without Tc and Pm), almost half (27) are allotropic at ambient pressure: Li, Be, Na, Ca, Ti, Mn, Fe, Co, Sr, Y, Zr, Sn, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Yb, Hf, Tl, Th, Pa and U. Some phase transitions between allotropic forms of technologically relevant metals are those of Ti at 882 °C, Fe at 912 °C and 1394 °C, Co at 422 °C, Zr at 863 °C, Sn at 13 °C and U at 668 °C and 776 °C. Element Allotropes Tin grey tin (alpha tin, Tin pest ) white tin (beta tin) rhombic tin (gamma tin) sigma tin (forms at very high pressure) [6] Iron ferrite -iron): the ferromagnetic form at T < 770 °C (the Curie point , T C ); BCC crystal structure β -iron : T = 770 912 °C; the paramagnetic form of α -iron; same structure as α austenite -iron): 912 1,394 °C; FCC crystal structure δ -iron: 1,394 1,538 °C; forms from cooling down molten iron; same structure as α ε -iron (also called hexaferrum): forms at high pressures; HCP crystal structure Cobalt α -cobalt forms above 417 °C simple cubic (metallic) β -cobalt forms below 417 °C hexagonal close packed (hcp) (metallic) Polonium α -polonium simple cubic (metallic) β -polonium rhombohedral (metallic) Lanthanides and actinides o Cerium , samarium , dysprosium and ytterbium have three allotropes. o Praseodymium , neodymium , gadolinium and terbium have two allotropes. o Plutonium has six distinct solid allotropes under "normal" pressures. Their densities vary within a ratio of some 4:3, which vastly complicates all kinds of work with the metal (particularly casting, machining, and storage). A seventh plutonium allotrope exists at very high pressures. The transuranium metals Np, Am, and Cm are also allotropic. o Promethium , americium , berkelium and californium have three allotropes each. [7]
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~ Page 9 of 79 ~ ISOMORPHISM Existence of different substances in one crystalline form is known as "ISOMORPHISM". Or different substances may exist in identical crystalline forms. This phenomenon is called i somorphism and these substances are known as ‘Isomorphous’. Examples of isomorphic substances are given below: 1.
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