Atomprocent

Atomprocent, or atomic percent, is the percentage of atoms of a given element in a material. It is defined as p_A = (N_A / N_T) × 100, where N_A is the number of atoms of element A in the sample and N_T is the total number of atoms in the sample or phase considered. The sum of atomic percentages for all elements in a sample typically equals 100. In Swedish, atomprocent is the common term; in English, the equivalent is atomic percent.

Relation to other measures: The mole fraction x_A equals N_A / N_T, so atompercent equals 100 × x_A. If a composition is given as mass fractions w_i, the atomic percent is p_i = (w_i / A_i) / Σ_j (w_j / A_j) × 100, where A_i is the atomic weight of element i. This converts mass-based data into an atom-based composition.

Measurement: In practice, atomic percentages are derived from analytical techniques such as electron probe microanalysis (EPMA) and energy-dispersive X-ray spectroscopy (EDS) in electron microscopy, or from other spectroscopy and mass-based methods. These measurements may report atomic percent or weight percent and often require standardization, matrix corrections, and calibration to account for factors like atomic number, absorption, and fluorescence.

Applications: Atom percent is widely used in metallurgy, materials science, and crystallography to specify alloy compositions, non-stoichiometric compounds, and solid solutions. It is important for phase-diagram analysis, diffusion studies, and materials design where the exact ratio of atoms matters.

Limitations: In heterogeneous or multiphase materials, local atomic percentages can vary. Measurements can be biased by sample preparation, detection limits for light elements, and instrument response. Atomic percent is an idealized description that assumes well-defined counting of atoms.