A Study of the Phase Transition in the System [Ag_1−x(Na)_x]NO₃ by Infrared Spectroscopy

Abstract

A b s t r a c t . A complete infrared study of the mixed crystal system of AgNO, and NaNO, is carried out in the region 400-4000 em-'. The study includes internal fundamental normal vibrations of the NO-, ion in the ordered and disordered phases of AgNO, a t different values of the sodium concentration, the I.R. spectrit, spectral band shape intensities, and frequencies of t h r intrrnal modes as functions of the sodium ion concentration. Special attcntion is paid to bending mode, combination mode, asymmetric stretching mode, and over-tone. The rotation$ energy barrier is determined a t different concentrations of the sodium ions in the systrm. Eine Untersuchung der Phaseniibergange im System [Agl-,(Na),]NOs mittels InfrarotspcktroskopieI n h a l t s iibersicht. Es wird eine vollstandige IR-Untrrsurhitng drs Misc1ikrist;~llsystems aus AgNO, und NaNO, im Brreich zwischen 400 und 4000 rm-l durchgrfuhrt. Sie umfnI3t die inneren Grundschwingungen des NO-,-Ions in der geordneten nnd ungeordnetcn AgN0,-Phase und die 1R-Spektrencharakteristika bei unterschiedlichrn Na-Konzentrstionen. Dir Rotntionsencrgirbarrirre wird fur unterschiedliche Na-Konzentrationen im System bestimmt.

Infrared absorption spectra studies in (NaNO3–NaNO2) system

“…Figure 1 shows that NaNO 2 crystals ðx ¼ 0Þ have three internal fundamental normal vibrations at n 1 ¼ 1325 cm À1 , n 3 ¼ 1271 cm À1 and n 2 ¼ 825 cm À1 which are in agreement with those values calculated by Fahim [21]. The bending mode n 2 , which appears in the IR spectra as a sharp peak in pure NaNO 2 , remains a strong sharp peak as NO À 3 concentration is increased, and agrees with the bending mode of NaNO 3 , compare El-Kabbany et al [22]. The relative intensity of this mode was also increased due to increasing of concentration of NO À 3 ions as shown in Fig.…”

Novel Wide-Working-Temperature NaNO3-KNO3-Na2SO4 Molten Salt for Solar Thermal Energy Storage

“…It is clearly observed that the bands at about 716 cm −1 , 1050 cm −1 and 1358 cm −1 at 20 °C in the solid state of solar salt and TMS series of molten salts were attributed to the vibrations of NO3 − in KNO3.Furthermore, 727 cm −1 , 1070 cm −1 and 1386 cm −1 corresponded to NO3 − in NaNO3. Compared with 20 °C, at 300 °C, the characteristic peaks of NO3 − of the stretching vibration peaks in KNO3 and NaNO3 were changed into one peak at about 730 cm −1 and 1050 cm −1 because of the inhomogeneity and randomness of the ion cluster microstructure with increasing temperature [50], while weaker peak shapes at about 130-1440 cm −1 were not observed. This also illustrated that the arrangement of the cations around NO3 − was very uniform when the two systems were in a solid state [51,52].…”

A study of the thermal analysis of the solid solution (AgxK1−xNO3

“…As the average distance between the cations increases, any intercationic interactions must become progressively weaker and any correlations among the interactions of the cations with the structure must vanish. A simplified model is proposed below for the energy barrier of rotation of the NO 3 group in the mixed crystal system (AgxK1_x)NO 3, as shown in Fig. 7.…”

“…This is a calcite-like structure, but is characterized by disorder of the anions around their three-fold axis. In a previous work [3], we studied the order -disorder phase transition of AgNO 3 by means of IR spectroscopy (400-4000 cm -~) over a wide range of temperature (30-195~ KNOa undergoes a first-order phase transition from the ordered phase II (symmetry Da26-Pma) to the disordered phase I (symmetry D~-R3c) at 135~ [4] ( Fig. la).…”

“…This orthorhombic phase is a centrosymmetric structure which resembles neither the calcite nor the argonite structure. The high-temperature AgNO 3 modification is stable above 160~ The space group is R3m with rhombohedral cell dimensions arh=4.125 A, ct=78.1 ~ at 444 K and z = 1 [2,3]. This is a calcite-like structure, but is characterized by disorder of the anions around their three-fold axis.…”