Abstract
In our comprehensive crystallographic investigation of the quasi-binary Pr
2CuO
4-Sr
2CuO
3 system, we observe the structural evolution
T′→
T
∗→
T→
Sr
2
CuO
3
with increasing Sr substitution in P Pr
2−
x
Sr
x
CuO
4−δ, that is distinctly different from the behavior in Sr-dopped La
2CuO
4 or Nd
2CuO
4. From the results of structural refinement using neutron powder diffraction and valence study from PrL
3 X-ray absorption, we find that the stabilization of the T
∗ phase in Pr
1.6Sr
0.4CuO
4 is associated with the preferential occupation of large Sr ions in the T-type half unit cell and the presence of Pr ions in the T'-type half unit cell having an average valence larger than 3+. Furthermore, the presence of large in-plane oxygen deficiency is related to the stabilization of the T structure in Pr
1.0Sr
1.0CuO
3.6. Formal Cu valence in the T
∗ or T compound, deduced from an oxygen stoichiometry study using thermogravimetric analysis and neutron structural refinement, is larger than 2+; however, neither superconductivity nor metallic behavior is observed.