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Atomic ratio - Wikipedia

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The atomic ratio is a measure of the ratio of atoms of one kind (i) to another kind (j). A closely related concept is the atomic percent (or at.%), which gives the percentage of one kind of atom relative to the total number of atoms.[1] The molecular equivalents of these concepts are the molar fraction, or molar percent.

Mathematically, the atomic percent is

{\displaystyle \mathrm {atomic\ percent} \ (\mathrm {i} )={\frac {N_{\mathrm {i} }}{N_{\mathrm {tot} }}}\times 100\ } %

where Ni are the number of atoms of interest and Ntot are the total number of atoms, while the atomic ratio is

{\displaystyle \mathrm {atomic\ ratio} \ (\mathrm {i:j} )=\mathrm {atomic\ percent} \ (\mathrm {i} ):\mathrm {atomic\ percent} \ (\mathrm {j} )\ .}

For example, the atomic percent of hydrogen in water (H2O) is at.%H2O = 2/3 x 100 ≈ 66.67%, while the atomic ratio of hydrogen to oxygen is AH:O = 2:1.

Another application is in radiochemistry, where this may refer to isotopic ratios or isotopic abundances. Mathematically, the isotopic abundance is

{\displaystyle \mathrm {isotopic\ abundance} \ (\mathrm {i} )={\frac {N_{\mathrm {i} }}{N_{\mathrm {tot} }}}\ ,}

where Ni are the number of atoms of the isotope of interest and Ntot is the total number of atoms, while the atomic ratio is

{\displaystyle \mathrm {isotopic\ ratio} \ (\mathrm {i:j} )=\mathrm {isotopic\ percent} \ (\mathrm {i} ):\mathrm {isotopic\ percent} \ (\mathrm {j} )\ .}

For example, the isotopic ratio of deuterium (D) to hydrogen (H) in heavy water is roughly D:H = 1:7000 (corresponding to an isotopic abundance of 0.00014%).

Doping in laser physics

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In laser physics however, the atomic ratio may refer to the doping ratio or the doping fraction.

  • For example, theoretically, a 100% doping ratio of Yb : Y3Al5O12 is pure Yb3Al5O12.
  • The doping fraction equals,
{\displaystyle \mathrm {\frac {N_{\mathrm {atoms\ of\ dopant} }}{N_{\mathrm {atoms\ of\ solution\ which\ can\ be\ substituted\ with\ the\ dopant} }}} }
  1. ^ McGraw-Hill Dictionary of Chemistry. McGraw-Hill. 27 January 2003. pp. 31. ISBN 0-07-141046-5.