Thermal Conductivity of Gel-Grown Barium Oxalate at 326 and 335？K

Single crystals of barium oxalate have been grown by gel method using agar-agar gel as media of growth at ambient temperature. The grown crystal crystallizes under monoclinic structure. Thermal conductivity of gel-grown barium oxalate crystals as a function of temperature has been studied at 326 and 335？K by using divided bar method. The thermal conductivity of barium oxalate crystal at 326？K was found 3.685？W？m？1？K？1 and 3.133？W？m？1？K？1 at 335？K. The reduction of thermal conductivity with the rise in temperature may be due to reduction in mean free path of phonons in the solid. 1. Introduction A material possessing both very high and very low thermal conductivities has a wide range of applications. Solid materials like diamond and silicon have high thermal conductivity, and therefore they are used in thermal electronic devices [1–8]. Low thermal conductivity materials like skutterudites [9, 10], clathrates [11, 12], and Zintl phases [13] have high thermoelectric efficiency [14]. The thermal conduction in solid is directly correlated with the harmonicity and anharmonicity of thermal vibrations. Thus, materials possessing harmonic thermal vibrations are responsible for very high thermal conductivity, whereas anharmonic vibrations are attributed for low thermal conductivity. A number of factors like impurities, dislocations, and crystal boundaries contribute to thermal conduction in solids. Well facet prismatic, platy-shaped, transparent crystals were grown by gel method using agar-agar gel as media of growth at ambient temperature [15, 16]. Since barium oxalate is a pyronature material, which shows great promise in pyrotechnic and high temperature electronic applications [17, 18], it is therefore interesting to investigate the thermal properties such as thermal conductivity of this material. The quantity of heat that passes through a substance in unit time of unit area and unit thickness, when its opposite faces differ in temperature by one degree, is known as thermal conductivity. The SI unit of thermal conductivity is Watt per meter Kelvin . Measurement of thermal conductivity is an important property for investigating lattice defects or imperfection in solid. This property also provides an opportunity for investigating existing intriguing physical phenomenon, and therefore to study thermal conductivity of solid material is of great technological interest. In the present work, thermal conductivity of crystals as a function of temperature has been studied at 326 and 335？K. 2. Experimental Procedure The growth of barium oxalate was carried out in