Nanocalorimetry experiments were conducted in a N 2 atmosphere on an as-deposited amorphous film with initial CuP 2.5 composition, with an average heating rate of roughly 5000 °C/s. Temperature-dependent thermoelectric characterization (electrical and thermal conductivity and Seebeck coefficient) was performed in vacuum on three films with different compositions after annealing. The electrical conductivity was measured using the van der Pauw (vdP) method The Seebeck coefficient was measured with respect to platinum metals lines using an internal four-probe platinum thermometer. The thermal conductivity was derived from the current-voltage characteristics of membrane heaters/thermometers in the self-heating regime. The hole concentration and mobility were measured on the same samples by double AC Hall. More details on all measurements are available in the Supporting Information.