ENTHALPIES OF FORMATION FOR GROUP-IV SELENIDES (GESE2, GESE2(AM), SNSE, SNSE2, PBSE) BY DIRECT-COMBINATION DROP CALORIMETRY

We have determined the enthalpies of formation for GeSe2(cr), SnSe2(cr), SnSe(cr), and PbSe(cr) and for amorphous GeSe2 using direct-combination drop calorimetry. Our results are as follows: DELTA(f)H(m)-degrees(GeSe2, cr, 298 K) = -84.4 +/- 1.8 kJ mol-1, DELTA(f)H(m)-degrees(GeSe2, am, 298 K) = -76.5 +/- 1.0 kJ mol-1, DELTA(f)H(m)-degrees(SnSe2, cr, 298 K) = -126.9 +/- 1.6 kJ mol-1, DELTA(f)H(m)-degrees(SnSe, cr, 298 K) = -93.8 +/- 3.3 kJ mol-1, and DELTA(f)H(m)-degrees(PbSe, cr, 298 K) = -96.3 +/- 1.1 kJ mol-1. From our results for DELTA(f)H(m)-degrees(GeSe2, cr, 298 K) and DELTA(f)H(m)-degrees(GeSe2, am, 298 K), we have calculated the enthalpy of the process GeSe2(am) --> GeSe2(cr) to be (-7.9 +/- 2.1) kJ mol-1.