Elastic energy and line directions of grown-in dislocations in KDP crystals

The orientation factor, K, of elastic dislocation energy is calculated for dislocations in KDP (space group I42d) with Burgers vectors b = 〈100〉, [001], 〈110〉, 〈011〉, and 1/2〈111〉. As a result of elastic anisotropy, for dislocations with b = 〈110〉, K has an absolute maximum in pure screw orientation. The preferred line directions characterized by a minimum elastic energy per unit growth length, W, are calculated for nine types of dislocations in (011) and (010) growth sectors; seven of them are identified by X-ray topography. The agreement of observed and calculated line directions is satisfactory except for dislocations with b = [011] in the (011) growth sector. Because of W having a very weak minimum in this case, it is suggested that the position that the position of these dislocations is influenced by a variation of dislocation core energy with direction that has been neglected in the calculations.