Order-disorder structural phase transition in the system of intercalated Ni atoms in the Ni$_{0.5}$TiSe$_2$ compound

Changes in the crystal structure of the Ni$_{0.5}$TiSe$_2$ intercalated compound have been thoroughly investigated using powder X-ray diffractometry in the temperature range from 93 to 700 K. It has been shown that upon heating to the temperature of about 400 K, this compound undergoes a phase transition from the monoclinic structure described by space group $I12/m1$ to the trigonal structure $(P\bar3m1)$, which is associated with the disorder in the subsystem of intercalated Ni atoms. The supercooling effect with the formation of the metastable state, which is characteristic of first-order phase transitions such as melting and crystallization, has been revealed in the region of the order-disorder phase transition, and the anomalous behavior of the resistivity has been observed.