Lanthanum-stimulated high-temperature whisker growth of α-SiC

• Published in: Journal of crystal growth 1972-01, Vol.12 (2), p.97-105
• Main Authors: Verspui, G., Knippenberg, W.F., Bootsma, G.A.
• Format: Article
• Language: English
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/0022-0248(72)90037-1

A study has been made of the growth and morphology of α-SiC whiskers obtained by the effect of lanthanum on silicon carbide crystals growing into a cavity in a SiC mass, heated in an inert ambient of 1 atm pressure, at temperatures between 2300 and 2600 °C. The morphology and the growth rates of the ribbonlike 6H- whiskers are compared with the corresponding properties of the almost equilateral hexagon-shaped plane- parallel platelets of 6H SiC obtained in the same conditions, except for the presence of lanthanum. The addition of lanthanum causes the growth of thinner elongated crystals with an increased growth rate in the longitudinal direction and a decreased rate of growth in width. For platelets and ribbons the activation energies associated with the increase of the growth rates with increasing temperature are the same (∼ 130 kcal/mole) for the two growth directions within experimental accuracy. Platelets and ribbons are both bounded by large-area basal faces {0001} and first-order prismatic and pyramidal side faces {10 i l}; the tips of whiskers interrupted in their growth are rounded and show both first-order faces {10 i l} and second order faces {11 2 l}. The effect of lanthanum is understood as an adsorption-blocking effect on the {10 1 l} side faces favouring ao. {11 2 l} faces of rapid growth at the tip of whiskers.