Positron annihilation study of spin-crossover in [Fe x Zn1−x (ptz)6](BF4)2 single crystals

Positron lifetime measurements were carried out on [Fe x Zn1−x (ptz)6](BF4)2 single crystals in the temperature range of 72–300 K. Complementary Doppler broadening spectra were also recorded at room temperature. The probability of the formation of o-Ps (lifetime 500–1400 ps) was between 10–30%. Both the spin density and the lattice parameters of the sample affected the lifetime of o-Ps through the ortho-para conversion and the pick-off annihilation, respectively. The positron annihilation technique proved to be a sensitive detector of the spin-crossover5T2 ↔1A1 and of the concomitant phase transformation.