The low-temperature transition in magnetite

Magnetite was shown to transform from the cubic to the orthorhombic system at temperatures below 119 deg K. The thermal expansion coefficient of the c axis became negative below 119 deg K, and at about 95 deg K there was no appreciable difference in the spacing of (440) and (008). The dimensions of the magnetite unit cell were measured at 295 deg, 128 deg, and 78 deg K and the resulting volumes were 591.4, 589.1, and 589.6 A to the power of 3, respectively. From these data and the c-axis length at 108 deg K, the coefficients of thermal expansion above and below the transition were calculated.