Silver iodide (silver iodide)

Japanese: ヨウ化銀(沃化銀) - ようかぎん（英語表記）silver iodide

Chemical formula: AgI. Yellow solid. Specific gravity: 5.67, melting point: 552°C, boiling point: 1506°C. Unlike other silver halides, it takes on a sodium chloride structure only under high pressure, but is polymorphic at normal pressure. The α form is stable at room temperature and is zinc-smelt type (cubic crystal system, lattice constant a = 6.48 Å). It has a transition point at 137°C and becomes the wurtzite type β form. The β form is hexagonal crystal system, a = 4.59 Å, c = 7.52 Å. When AgI is precipitated under conditions of excess ^I-, the β form, which is metastable even at room temperature, is obtained, but when rubbed, it changes to the α form.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

化学式AgI。黄色固体。比重5.67，融点552℃，沸点1506℃。他のハロゲン化銀と異なり，高圧でのみ塩化ナトリウム型構造をとるが，常圧では多形を示す。α形は常温で安定でセン亜鉛鉱型(立方晶系，格子定数a＝6.48Å)である。137℃に転移点がありウルツ鉱型β形となる。β形は六方晶系，a＝4.59Å，c＝7.52Åである。I^－を過剰の条件でAgIを沈殿させると常温でも準安定状態のβ形が得られるが，これをこするとα形に変わる。

出典　株式会社平凡社世界大百科事典第２版について　情報

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