BCZYx samples were prepared by a modified version of citrate-nitrate combustion synthesis with subsequent decomposition of organometallic complexes at high temperatures.
Prior to the synthesis, the starting materials (Ba(NO3)2,Ce(NO3)3$6H2O, Y(NO3)3$6H2O, CuO, Co3O4 and citric acid, with purity no less than 99.5%),
were thoroughly mixed and dissolved afterward in a solution containing stoichiometric required amounts of Zirconium oxynitrate and glycerin.
Citric acid and glycerin were chosen as chelating and complexing agents with the appropriate molar ratio to metal nitrates (0.5:1.5:1, respectively).
The as-obtained solutions were heated and stirred at 100 C for 0.5 h
with subsequent addition of ammonium hydroxide to ensure pH at the level of 8e9.
The final solution was again heated at 250 C to evaporate the excess water
and assist in foaming of a viscous gel, which was eventually autoignited.
The obtained gray (for low Zr content) or black (for high Zr content)
powders were subsequently fired at 700 C (1 h) in air to remove organic residue,
and then the light-colored ones were calcined at 1150 C (5 h)
to form single-phase products. The powders were milled in a planetary mill
(Fritsch Pulverisette 6) for 1 h at 250 rpm,
uniaxially pressed into thepellets under 4 ton cm2 and then sintered at 1450 C for 5 h.