An electronic transition from a high-spin state to a low-spin state, or vice versa. Example: With an increase in temperature
Co3+ ions in
LaCoO3 transform from a low-spin state (t 2g 6 e g 0) to the high-spin state (t 2g 4 e g 2).
Source:
PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 591 (https://doi.org/10.1351/pac199466030577)