In the literature, the density value of nickel (II) oxide (NiO) at room temperature can be found as 6.67 or 6.72 gr/cm3. It is expected that the density value will decrease as the temperature increases. I could only find one study(Touloukian, 1966) that gave a graph of the density of NiO with temperature (the density values are given as 7.45 and 7.33 gr/cm3 for 300 K and 700K, respectively).

I would appreciate it if you could suggest any source that shows the density-temperature graph for NiO.