Nanoindentation of melt-extracted amorphous YAG and YAG:Eu, Nd micrometric fibers synthesized by the citrate precursor method

We report the structural and mechanical characterization of yttrium aluminum garnet fibers obtained with Eu and Nd additions by the melt-extraction method (ME). Powders were synthesized by the modified citrate precursor method. This method produces in a single step of heat treatment the pure YAG phase avoiding the formation of YAlO3, Y4Al2O9 or Y2O3 phases. Rare earth additions delay proportionally to the added quantity of dopant the crystallization temperature of the YAG phase. Using crystalline powders, cylindrical fibers (20–30 μm) in an amorphous state irrespective of doping type and amount were obtained by ME. Nanoindentation tests were carried out showing hardness and reduced elastic modulus of 5.8 ± 0.3 and 79.3 ± 4.9 GPa for pure YAG fibers, respectively. 2 at.% additions of Nd to the YAG phase lead to an increment in hardness and reduced elastic modulus (9.1 and 128.6 GPa, respectively). However, further increments of Eu or Nd (5 at.%) cause a clear degradation of the mechanical properties respective to the values reached with 2 at.% of rare earth additions. This degradation effect seems to be correlated to the atomic interaction due to difference between radii of Eu and Nd, respective to Y.