Synthesis, characterization, mechanical and magnetic characteristics of Gd³⁺ /PO₄ ^{3 -} substituted zircon for...

The study reports on the use of sol-gel technique to yield zircon type [Zr_(1-0.1-x) GdxTi_0.1 ] [(SiO₄ )_1-x (PO₄ )_x ] solid solution. Titanium has been used as a mineralizer to trigger zircon formation while equimolar concentrations of Gd³⁺ and PO₄ ^3- were added to determine their accommodation limits in the zircon structure. The crystallization of t-ZrO₂ as a dominant phase alongside the crystallization of m-ZrO₂ and zircon were detected at 1200°C while their further annealing revealed the formation of zircon as a major phase at 1300°C. Heat treatment at 1400°C revealed the formation of zircon-type solid solution [Zr_(1-0.1-x) Gd_x Ti_0.1 ][(SiO₄ )_1-x (PO₄ )_x ] comprising the accommodation of 10 mol.% of Gd³⁺ /PO₄ ^3- at the zircon lattice. Beyond 10 mol.% of Gd³⁺ /PO₄ ^3- , the crystallization of GdPO₄ as a secondary phase is noticed. Structural analysis revealed the expansion of zircon lattice due to the simultaneous occupancy of Gd³⁺ /PO₄ ^3- for the corresponding Zr⁴⁺ /SiO₄ ^4- sites. The mechanical strength of single-phase zircon solid solution was higher in comparison to that of multiphase materials, namely in the presence of GdPO₄ formed as a secondary phase in samples with added equimolar Gd³⁺ /PO₄ ^3- contents beyond 10 mol.%. Nevertheless, the paramagnetic behavior of the samples demonstrated a steady surge as a function of enhanced Gd³⁺ content.