Spontaneous strain at the structural phase transition in NaNO 3

摘要: The temperature dependence of the hexagonal c unit cell parameter high-purity NaNO3 shows an anomaly at 553 K corresponding to orientational ordering transition. a is barely influenced by single component spontaneous strain for this zone boundary instability large (∼55×10−3 295 K), and couples quadratically with order parameter. critical exponent β found have value 0.22 ± 0.01, which differs from that expected in classical case. Below ca 450 K, crossover tricritical behaviour observed (β=1/4). evolution macroscopic as revealed follows between 70 K. At temperatures below saturation observed. Combined recent data specific heat measurements, exponents suggest three-dimensional, three-states Potts model may describe Precursor above T c consistent local result fluctuations associated antiordered NO3 group pair configuration.