ETCHING AND X-RAY TOPOGRAPHY OF FLUX-GROWN MAGNETIC GARNETS

Internal growth defects of high-quality garnet crystals were studied by selective etchants and Lang x-ray transmission topography. Terminal growth sections contained the fewest defects and dislocation densities were 10 2-104/cm2. Internal sections revealed both randomly dispersed etch pits and linear arrays. The latter were frequently found in the form of parallel grids. Results indicated that {100}, {111}, {411}, and {105} were the defective planes. X-ray topographs verified that parallel linear faults are present in crystals on these same planes. The faults are not dislocation lines but tubular structural deviations caused by flux precipitation or other compositional changes. The origin and arrangement of the internal faults are related to fluctuations of the crystal growth rate. The rate changes can be initiated by small thermal gradients in the solution. © 1969 The American Institute of Physics.