resumo
In order to study the crystal structure, phase relationships, and magnetic properties of the system Tb5-xLaxSi2Ge2, a series of polycrystalline samples with compositions ranging from x = 0 to x = 5 have been synthesized and characterized in detail. At room temperature, two structures have been detected: Compounds in the concentration range 0 <= x < 1 present a monoclinic Gd5Si2Ge2-type structure, while for x > 1 a tetragonal Zr5Si4-type structure is observed. The unit cell volume increases linearly with La concentration but with two different slopes: similar to 18 angstrom(3)/x and similar to 33 angstrom(3)/x for 0 <= x < 1 (monoclinic) andx > 1 (tetragonal), respectively. In the monoclinic region, an increase of T-C was observed, reaching a maximum value of T-C similar to 154 K, at the x = 0.75 composition. This feature is explained based on specific La occupancy at the R2 site which was supported by density functional calculations for low La concentration. The samples that crystallized in the tetragonal structure exhibit a linear decrease of T-C(x) with a slope of partial derivative T-C/partial derivative x similar to -38 K/x, reaching 0 K for the x = 5 composition. A magnetic and structural x-T phase diagram of the Tb5-xLaxSi2Ge2 system in the temperature range 4-300 K is proposed.
palavras-chave
CRYSTAL-STRUCTURE; TRANSITION; GE; GD-5(SIXGE1-X)(4); ALLOYS; PHASES; SI; TT
categoria
Physics
autores
Belo, JH; Pereira, AM; Araujo, JP; de la Cruz, C; dos Santos, AM; Goncalves, JN; Amaral, VS; Morellon, L; Ibarra, MR; Algarabel, PA; Magen, C
nossos autores
João Nuno Santos Gonçalves
Investigador Júnior
Vitor Brás Sequeira Amaral
Professor CatedráticoProjectos
agradecimentos
This work was partially supported by the projects POCI/CTM/61284/2004, PTDC/CTM-NAN/115125/2009, FEDER/POCTI No. 155/94 from Fundacao para a Ciencia ex Tecnologia (FCT), Portugal. A. M. P. thanks FCT for Grant No. SFRH/BPD/63150/2009. J.N.G. thanks FCT for Grant No. SFRH/BPD/82059/2011. Part of this research was performed at the High Flux Isotope Reactor at the Oak Ridge National Laboratory, which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. C. M. acknowledges the support of the Fundacion ARAID. The financial support of the Spanish MEC (MAT2008-06567-C02) and DGA (Grant No. E26) is acknowledged. This research was supported by UT Battelle, LLC, under Contract No. DE-AC05-00OR22725 for the US Department of Energy, Office of Science.