Thermal properties of K2Ba(NO2)4

M. Chabin, F. Gilletta, Y. Luspin, G. Hauret
1982 Journal de Physique  
2014 Nous avons mesuré la chaleur spécifique de monocristaux de nitrite de baryum et potassium K2Ba(NO2)4 entre 130 K et 435 K. Il apparait deux transitions, respectivement à 208,6 K et 428 K. La transition basse-température présente les caractéristiques d'une transition du second ordre et l'excès de chaleur spécifique est caractérisé par les exposants critiques 03B1 = 03B1' = 0,60 ± 0,03. La transition haute-température apparait à quelques degrés de la décomposition de K2Ba(NO2)4 et ne peut
more » ... NO2)4 et ne peut être complètement étudiée. Abstract. -The specific heat of single crystals of potassium baryum nitrite K2Ba(NO2)4 has been measured between 130 K and 435 K. There are two transitions at 208.6 K and 428 K, respectively. The low temperature transition exhibits second order features and the excess specific heat is characterized by critical exponents 03B1 = 03B1' = 0.60 ± 0.03. The high temperature transition occurs a few degrees below the decomposition temperature and so cannot be studied in detail. J. Physique 43 (1982) 337-339 FTVRIER 1982, Classification Physics Abstracts 77.80B -65.40 1. Introduction. -Little [1-6] has been published on the properties of potassium baryum nitrite K2Ba(N02)4. Their crystallographic properties at room temperature were first described a long time ago by Fock [1]. More recently, IvanQv [4] reported optical, dielectric and ferroelastic properties of K2Ba(N02)4 and pointed out that this crystal undergoes a phase transition in the vicinity of 146 ~C between a high temperature hexagonal phase 6/mmm (a phase) and an orthorhombic mmm phase (j8 phase) stable below 146 ~C. Moreover, from birefringence measurements, he suggests that a second phase transition takes place in the vicinity of -70 ~C between the orthorhombic ~i phase and a third phase (y phase). It is suggested that the high temperature transition ( T ~ 146 ~C) is second order [4] whereas there is no information relating to the character of the low temperature phase. We have investigated the thermal properties of K2Ba(N02)4 over a large range of temperature, in order to clarify the existence and type of the low temperature phase transition suggested by Ivanov [4].
doi:10.1051/jphys:01982004302033700 fatcat:lhwea5yhjzbynoj6ytuxz5as6i