Experimental method for determining surface energy anisotropy and its application to magnesia

An experimental technique has been developed to determine the surface energ y anisotropy of crystalline solids. The technique is based on atomic force microscopy measurements, which are used to quantify the geometry of thermal grooves, and electron backscattered diffraction pattern measurements, whic h are used to specify crystallographic orientations. Observations are made at circumferential thermal grooves, where it is assumed that Herring's loca l equilibrium condition for a triple junction holds and that the grain-boun dary energy is independent of its boundary plane. A truncated double Fourie r series is used to approximate the surface energy, and the unknown coeffic ients of the series are determined by fitting the observations to the local equilibrium condition. The method, which should be applicable to most poly crystalline materials, has been tested on magnesia that has been thermally grooved at 1400 degrees C in air. The maximum of the best-fit surface energ y function is at (111) and the minimum is at (100), The relative surface en ergies of the low-index planes are gamma(110)/gamma(100) = 1.040 +/- 0.008 and gamma(111)/gamma(100) = 1.072 +/- 0.010.