On the use of powder diffractometry in the study of phase transitions case of NaNO2

Abstract

The phase transition of NaNO2, is investigated by using X‐ray powder diffractometry. The temperature dependence of the lattice constants, peak intensities, and the order parameter of the ferroelectric phase, in the range of 27 to 200 °C, show the same results as obtained by using single‐crystal diffractometry. These experimental findings imply that the X‐ray powder method is suitable for the study of phase transition. The analysis of the powder diffraction profile would even improve the method.

Ferroelectric phase transitions in sodium nitrite nanocomposites

“…This value of β is in a good agreement with the value (0.362±0.004) obtained for the 3D-Ising model [20], by computer simulation of finite-size scaling for a second order PT. The curve η(T) for CFM for the 20 nm porous glass differs principally from those for nanocomposites with 3 and 7 nm pores and looks similar to the dependence obtained for the bulk [19]. Keeping in mind the results of the dielectric study of sodium nitrite within opal [7], where two types of nanocaverns exist with characteristic sizes from 70 nm up to 120 nm (and in which the authors observed a temperature hysteresis of the dielectric permittivity), and our results for the size of nanoparticles and their temperature dependence of the order parameter, one can conclude that at nanoparticle sizes smaller than 50 nm a crossover from a first order PT to a second order one takes place.…”

“…It is known [19] that the dependence of the intensity of diffraction peaks on the structure factor for sodium nitrite can be written in the following form…”

Анализ структуры и диэлектрического отклика композитов (1-x)NaNO-=SUB=-2-=/SUB=-+xBaTiO-=SUB=-3-=/SUB=- при x=0.05 и 0.1

“…На вставке показаны температурные зависимости интегральной интенсивности, нормированной на значение при комнатной температуре, пиков (022) (кружки) и (121) (квадраты). Температурные зависимости параметра порядка η(T ) чистого NaNO 2[14] (сплошная линия) и композита с x = 0.1 (точки, штриховая линия -результат процедуры сглаживания). На вставке приведены значения η(T ) при нагреве (темные кружки, сплошная линия) и охлаждении (светлые кружки) для композита.…”

Raman linewidths calculated as a function of temperature in NaNO2

“…1 Introduction Sodium nitrite, NaNO 2 , which is a ferroelectric material [1], undergoes an order-disorder phase transition at about 436.2 K [2]. Below this temperature, the structure of NaNO 2 is orthorhombic and is polar along the b-axis with space group 20 2v C -Immm [3], and it is in the ferroelectric phase.…”

“…We have also calculated the Brillouin frequencies close to the phase transition in NaNO 2 [51,52] using the experimental data for the thermal expansivity [15] and compared them with the experimental Brillouin frequencies [30]. Our calculation for the spontaneous polarization using the mean field theory [53] has been compared with the experimental data [2] for NaNO 2 in the ferroelectric phase. We have also studied the spectroscopic modifications of the Pippard relations for NaNO 2 in the paraelectric phase [54] and antiferroelectric phase with sinusoidal modulation of electric dipole moments [55].…”