No abstract

No abstract

It is well known that a paraelectric phase of NaNO~ crystals exists above 160 °C. Laue patterns with filtered Cu radiation obtained at 185 °C show, besides thermodiffuse spots, diffuse but relatively sharp layer lines orthogonal to the polar axis along l --2, 3, 4. It is shown that they can be explained by ca. 30/~ long small domains with ferroelectric structure (so called "cigarrillos") statistically orientated parallel or antiparallel to the polar axis. This positional disorder with correlations can never explain the observed continuous intensity of the first layer line near 002, even if correlated librations are introduced. Calculations and Fraunhofer patterns of two-dimensional models with statistical point structures prove that the domains oscillate parallel to the polar axis as rigid entities. The diffuse spots 030, 040 can furthermore be explained by cross-vibrating linear segments of the ferroelectric domains. Much of the analysis is carried out with the help of the Q-function calculated and experimentally produced from the models with a two-dimensional folding machine.

No abstract

No abstract