不純物








不純物（ふじゅんぶつ）とは、ある物質に、それ以外の物質が僅かに含まれている場合、その本来の物質以外の別の物質のことを指す。不純物は欠陥の一種である。一般には、不純物の存在は、本来の物質の性質を損なうことになる場合が多く、通常は不純物をいかに取り除くかに多くの努力が費やされる。ただ、一方では逆に不純物を利用して、本来その物質が持っていなかった新しい性質を引き出し、産業上有用な物質となる場合もある。



利用例


シリコンのような半導体においては、不純物を人工的に混ぜることにより、p型半導体、n型半導体を作ることができる。鉄がより強度の高い鋼になるのも不純物の効果による。また、不純物は物質の色（あるいは発光）に影響を及ぼすことがある。たとえば宝石において、主成分は同じ酸化アルミニウム（Al2O3, コランダム）だが、不純物の違いにより、サファイア（不純物：鉄、チタン）やルビー（不純物：クロム）となるのがこの場合である。



関連項目



  • 不純物準位

  • 物性物理学




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