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Why does electrical resistance usually increase when a conductor gets hotter?

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In metallic conductors, electrical resistance typically increases as temperature rises because of the behavior of the material's internal structure.

In a metal, electrons move through a crystal lattice to conduct electric current. While these electrons generally move to accommodate the host ions, they scatter when they encounter defects or irregularities in the lattice. As the temperature of the conductor increases, the ions within the crystal lattice vibrate with greater amplitude around their equilibrium sites.1

These increased vibrations effectively create more frequent "defects" or obstacles within the lattice structure. Consequently, the conduction electrons collide more often with these vibrating ions, which increases the rate of scattering. This heightened scattering hinders the mobility of the electrons, thereby increasing the resistivity and overall electrical resistance of the material.12