STUDIES OF PHASE TRANSFORMATIONS IN THE ND-LI-GE SYSTEM AT A TEMPERATURE OF 400 °C

Abstract

In this work, an isothermal section of the phase diagram of the state of the Nd-Li-Ge system was built on the basis of X-ray phase, microstructural and local X-ray spectral analyzes at a temperature of 400 °C in the range of 30–100 at.% Ge. For the synthesis of alloys, pieces of pure metals of a certain stoichiometric composition were compressed into tablets, which were placed in a tantalum crucible and heated to 400 °C. At this temperature, the alloys were held for two days, then the temperature was raised to 800 °C for one hour. Samples obtained during the experiment were annealed at a given temperature for six hours. Homogenizing annealing for all samples was carried out at 400 °C for 480 hours. Phase analysis of alloys was carried out by an array of X-ray diffraction data obtained using powder automated diffractometers DRON-2.0M (Fe Kα-radiation) and STOE STADI P (Cu Kα1-radiation). Quantitative determination of Lithium content was carried out by flame photometry using a Flapho-4 device. The phase composition of individual samples of the system was confirmed by energy dispersive X-ray spectroscopy (EDX) in combination with a raster electron microscope Tescan Vega 3 LMU. Identification, calculation and indexing of diffractograms, refinement of parameters of elementary cells was carried out using packages of LATSON, POWDER CELL-2.3 programs and WinCSD. Determination and refinement of the crystal structure by the powder method was performed using the FullProf 98 program. The results of the experimental study of the selected site showed the formation of a new ternary compound Nd2LiGe6 (structural type Pr2LiGe6, the Pearson symbol oS18, the space group Cmmm, a = 0.41657(1), b = 2.11079(5), c = = 0.43723(2) nm). The formation of a solid solution of Nd5LixGe3 (x = 0–0.4) was established due to the partial inclusion (up to x = 0.4) of Lithium atoms in the octahedral voids of the initial binary phase of the Nd5Ge3. Under the conditions of the experiment, the literature data on the formation of seven triple compounds were confirmed and the parameters of their elementary cells were clarified for all. The existence of NdLi2Ge and Nd2LiGe5 compounds at the temperature of the annealing proposed by us is not confirmed. The features of phase interactions of the triple system Nd-Li-Ge and other related systems containing rare earth metals, Li and Ge are considered. It is established that most of the phases synthesized in them crystallize in orthorhombic symmetry with known structural types of CaLiSi2, ZrNiAl, Ce2Li2Ge3, Tm4LiGe4 and Gd3Cu4Ge4.