resistivityconductivity

Resistivity (ρ) and conductivity (σ) are fundamental electrical properties describing how a material responds to an applied electric field. Resistivity quantifies the opposition to electric current flow, whereas conductivity measures the ease with which electric charge moves through the medium. They are inversely proportional: σ = 1/ρ, so low resistivity corresponds to high conductivity.

In the International System of Units (SI), resistivity is expressed in ohm‑meters (Ω·m) and conductivity in siemens per meter (S/m). The values span many orders of magnitude: typical metals such as copper have ρ ≈ 1.7×10^−8 Ω·m (σ ≈ 5.9×10^7 S/m), while insulators like glass have ρ ≈ 10^10–10^14 Ω·m (σ ≈ 10^−10–10^−14 S/m). Semiconductors occupy an intermediate range, for example silicon at room temperature has ρ ≈ 10^3 Ω·m (σ ≈ 10^−3 S/m) when intrinsic.

Resistivity depends on temperature and material purity. In metals, increasing temperature raises resistivity due to lattice vibrations, whereas in semiconductors, higher temperature generally reduces resistivity by generating carriers. Anisotropic crystals exhibit tensorial resistivity where different crystallographic directions have distinct values.

Measurement techniques vary with the material class. Bulk specimens often use a four‑probe method, where a known current is driven through outer contacts and voltage drop measured between inner contacts, minimizing contact resistance effects. Thin films employ van der Pauw geometry or the Hall effect for sheet resistance and carrier concentration. Cold‑rolled metals may have their resistivity inferred from conductivity measurements in magnetic fields.

Understanding resistivity and conductivity enables the design of efficient conductors, insulation systems, and electronic devices, and serves as a diagnostic tool for material purity, crystallinity, and temperature behavior.