Heat capacity of silicon in the range 350-770 K

The measurements of the specific heat of silicon were carried out using the DSC method. The single-crystal silicon, containing 5.5x10(17) cm(-3) of ox ygen, was the subject of our study. The measurement error was 5%. The tempe rature range of the measurements was 350-770 K. The scan rates were 4 or 16 KI min. Slow heating at 4 K/min shows an abnormality in temperature depend ence of the heat capacity in the range 550-680 K. The recorded curve resemb les a lambda -shaped curve characteristic of 2nd-order phase transitions. A t a higher scan rate, C-p (T) is a monotonic function, which is identical t o the data recommended in reference books. We assumed a possible mechanism of the observed phenomenon. When a crystal of silicon is heated, stressed z ones arise along subgrain and domain boundaries due to the anisotropy of th ermal expansion. The new high pressure phase of silicon with the structure of white tin (or Si-II) can be formed in these zones. The appearance releas es stress and stops the further growth of precipitates. According to our es timate, the concentration of the newly-formed phase is about 5 vol.%. Heati ng at higher rates does not cause similar phenomena.