Application of Vegard´s Law to the estimation of microstructural parameters in crystalline AB5´-based intermetallics

B.A.TALAGAÑIS; M.R ESQUIVEL.; G. M EYER

Ciudad de Buenos Aires

Congreso; ISMANAM 2008-XV International symposium on Metastable, Amorphous and Nanostructured Materials; 2008

Fernando Audebert-Laura Damonde-Facultad de Ingenieria-UBA

Mechanical alloying (MA) is a simple method used to obtain AB5-based compounds. Among, others, the following paths can be used: A + 5B                =                  AB5       (I)  or AB5´ + AB5´´        =                AB5      (II) The path (II) has the advantage that a better quality control of the AB5 final chemical composition is achieved. No preferential lamination, typical of mixtures of metals, occurs when mixtures of intermetallics are mechanically alloyed.   But samples obtained by MA are obtained either as an amorphous, nano or micro-crystalline structure with a low quality X-ray diffraction (XRD) pattern and no conclusion regarding the microstructural parameters can be done. But the quality of the XRD patterns of both reactants and products can be improved by low temperature annealing (T £ 600ºC). Since the structures of AB5´s have the same space group (P6/mmm), the micro structural parameters can be estimated from the cell parameters a and c by establishing a correlation for each of them using an approach based on Vegard´s Law [1]. In this work, various AB5 with different contents of Lanthanide element (La,Ce,Nd,Pr)    in the A-site and with the same element (Ni) in the B-site of the intermetallic were mechanically alloyed and annealed at 600 ºC during 24 h. Lanthanide initial composition was determined by Neutron Activation Analysis (NAA). AB5 samples obtained were analyzed by XRD and energy dispersive spectroscopy (EDS). Cell parameters were determined by Rietveld refinements and results were compared to the correlation based on Vegard´s Law. From these results, the lanthanide distribution in the corresponding crystallographic sites is discussed and correlated to the path of synthesis used. References: [1]  L.A. Girifalco, Acta Metallurgia, 24, 8, (1976), 759-771.