Study of long and short range order in ferroelectrics by optical secondharmonic generation

摘要: Abstract The relation between optical second harmonic generation (SHG) and ferroelectric order is discussed in the case of NaNO2. nonlinear susceptibility χNL determining SHG state shows decrease long range NO 2 -sublattice approaching Curie point. In disordered paraelectric third-rank tensor vanishes has to be described by a χN fourth rank, interpreted as measure short order. Its temperature dependence reveals an anomaly at 207°C, also shown thermal expansion coefficients.