STUDIES ON THE COOPERATIVE PHENOMENON OF X-RAY CRITICAL. SCATTERING NEAR PHASE TRANSITIONS IN SOLIDS

摘要

The disorder of the pyroeiectric phase of NaN0 has .been evidenced from the existence at about 185°C of x-ray diffuse scattering sheets nor mal to the polar axis. It has been shown that these sheets can be explained as arising from long small domains (so called "cigarillos) of "about 30 A with ferroelectric structure statistically oriented parallel or antiparcaliel to the polar axis. This positional disorder alone with correlations cannot explain the observed diffuse scattering sheet near to the 002 reflection, even If correlated iterations are Introduced. Calculations and Fraunboier patterns of two dimensional models with statistical point structures prove that the domains oscillate parallel to the polar axis as rigid entitles. Much of the analysis has been carried out with the help of the Q-function calculated and experimentally produced with a two-dimensional folding machine.