In reply to Eric Walker's message of Mon, 16 Mar 2015 21:32:43 -0700: Hi Eric, [snip] >On Mon, Mar 16, 2015 at 2:37 PM, <mix...@bigpond.com> wrote: > >If all the nuclei move in unison, then they can be hot (i.e. vibrating), >> yet in >> their own frame of reference they are all stationary with respect to one >> another. > > >What causes the atoms to move in unison, in contrast to normal, chaotic >movement? > >Eric
The notion I had at the time was that an asymmetric crystal would have different distances between atoms in different directions. If a crystal could be found that had a shortest (longest) distance in only one direction, then there would be a preferential vibrational direction. Chains of atoms tend naturally to vibrate in unison (less harassment from the neighbors ;) I also thought that this situation might be more likely at a temperature near/at a phase transition in the material. Another thought was that ultrasonic vibrations (which tend to enforce vibration in unison upon the lattice) might help. In that case the amplitude of the enforced vibrations would need to be much larger than the normal thermal vibration amplitude, so that the latter was overwhelmed. The atoms don't all have to move in unison, as long as enough do to be effective. Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/project.html
