A new tetragonal phase in La-rich Pr_2-xLa_xCuO₄ (1.35 < x < 1.5)

Comprehensive X-ray diffraction study on the sub-solidus phase diagram in Pr₆O₁₁-La₂O₃-CuO system firstly revealed a new phase of Pr_2-xLa_xCuO₄ for 1.35 < x < 1.5. The phase has a tetragonal symmetry similar to the well-known T′-type structure (0 < x < 0.9). However, the lattice constants of both a and c are clearly distinct between the two tetragonal phases. The new phase coexists with the T′-phase for 0.9 < x < 1.3 and with the orthorhombic T-phase for 1.5 < x < 1.6. The sintered pellet of the new phase instantly transforms into fine powder (∼10 μm) upon cooling from synthesized temperature to room temperature without any compositional phase separation.