I always thought crystals with dislocations were used to mark the band edge frequencies. ... Martin VE3OAT - - - - - - - - - - - - - - - - - - On Sun, 22 Apr 2018 11:34:30 -0600 djl wrote : > > Darn. maybe not grain boundaries, but dislocations? or both? > Don > - - - - - - - - - - - - - - - - - - -