A triclinic phase of relaxor La-modified Pb(Zr0.65Ti0.35)O3 and its structure at 40 K by high-resolution neutron diffraction

The phase transitions and structure of 7% La-modified Pb(Zr0.65Ti0.35)O3 (PLZT 7/65/35) at 40 K were investigated using high-resolution powder diffraction. The high-resolution data suggest the existence of an alternate phase, which is not expected from the widely accepted phase diagram. By structural analysis and Rietveld refinement, the space group of this phase was determined to be F1 (the standard setting is P1 by adding face-centered generators), rather than the expected R3c or the reported Cm phase. The unit cell of this phase is deduced by doubling the primitive cubic cell along three main axes, cell parameters area a=8.14546(13) A, b=8.18539(15) A, c=8.16785(11) A, and interaxial angles are α=90.1925(24)°, β=89.8785(26)°, and γ=90.1564(34)°. The tilting system of oxygen octahedra is ābc instead of āāā in the R3c phase. The cation displacements and polarization are described in detail. The polarization direction was found to be along 〈112〉, not the main axes. The phase relationship and domain morp...