Magnolia lacandonica (subsection Talauma, Magnoliaceae), a new rainforest species from Chiapas, Mexico

Microstructural, magnetothermal and dielectric properties of YCrO 3 powders prepared by combustion and solid state methods have been studied by a combination of XRD, specific heat, magnetization and permittivity measurements. The TEM and XRD characterization confirm that the combustion powders are amorphous plate-like agglomerates of nano-sized crystalline particles. A more uniform grain size along with an increase of the relative density is observed by SEM in the sintered samples prepared by combustion route with respect to those produced by solid state reaction. Similar to the material obtained through solid state synthesis, the material prepared by the combustion method also shows spin canted antiferromagnetic ordering of Cr3 (S=3/2) at ?140 K, which is shown by magnetization as well as ?-type anomaly in the total specific heat. Furthermore, the magnetic contribution to the total specific heat reveals spin fluctuations above TN and a spin reorientation transition at about 60 K. Both YCrO3 compounds show a diffuse phase transition at about 450 K, typical of a relaxor ferroelectric, which is characterized by a broad peak in the real part of the dielectric permittivity as a function of temperature, with the peak decreasing in magnitude and shifting to higher temperature as the frequency increases. The relaxor dipoles are due to the local non-centrosymmetric structure. Furthermore, the high loss tangent in a broad range of temperature as well as conductivity analysis indicates a hopping mechanism for the electronic conductivity as we believe it is a consequence of the outer d3-shell, which have detrimental effects on the polarization and the pooling process in the YCrO 3 bulk material. The more uniform particle size and higher density material synthesized through the combustion process leads to an improvement in the dielectric Properties. " 2010 Elsevier Inc. All rights reserved.",,,,,,"10.1016/j.jssc.2010.06.001",,,"http://hdl.handle.net/20.500.12104/42646","http://www.scopus.com/inward/record.url?eid=2-s2.0-77955469536&partnerID=40&md5=f5cbdd6854727d56d41012e138b8ee30",,,,,,"8",,"Journal of Solid State Chemistry",,"186