The grain boundary groove shapes for equilibrated solid neopentylglycol (NPG) solution (NPG-26 mol% AMPD-4 mol% SCN) in equilibrium with the succinonitrile (SCN)-neopentylglycol (NPG)-aminomethylpropanediol (AMPD) liquid (NPG-45 mol% SCN-2.9 mol% AMPD) have been directly observed by using a horizontal linear temperature gradient apparatus. From the observed grain boundary groove shapes, the Gibbs-Thomson coefficient (Gamma) and solid-liquid interfacial energy (sigma(SL)) of solid NPG solution have been determined to be (7.8 +/- 0.8) x 10(-8) K m and (8.1 +/- 1.2) x 10(-3) J m(-2), respectively. The grain boundary energy of solid NPG solution has been determined to be (15.8 +/- 2.5) x 10(-3) J m(-2) from the observed grain boundary groove shapes. The ratio of thermal conductivity of equilibrated liquid to thermal conductivity of solid NPG solution has also been determined to be 0.42. (C) 2012 Elsevier B.V. All rights reserved.