Low-temperature phases in $\mathrm{Pb}{\mathrm{Zr}}_{0.52}{\mathrm{Ti}}_{0.48}{\mathrm{O}}_3$: A neutron powder diffraction study

A neutron powder diffraction study has been carried out on $\mathrm{Pb}{\mathrm{Zr}}_{0.52}{\mathrm{Ti}}_{0.48}{\mathrm{O}}_3$ in order to resolve an ongoing controversy about the nature of the low-temperature structure of this strongly piezoelectric and technologically important material. The results of a detailed and systematic Rietveld analysis at $20\mathrm{K}$ are consistent with the coexistence of two monoclinic phases having space groups Cm and Ic, respectively, in the approximate ratio 4:1, and thus support the findings of a recent electron diffraction study by Noheda et al. [Phys. Rev. B 66, 060103 (2002)]. The results are compared to those of two recent conflicting neutron powder diffraction studies of materials of the same nominal composition by Hatch et al. [Phys. Rev. B 65, 212101 (2002)] and Frantti et al. [Phys. Rev. B 66, 064108 (2002)].

Figure 1

PZT phase diagram as originally proposed by Jaffe et al. in Ref. 1 (open circles) with the modifications reported by Noheda et al. in Ref. 6 (full circles). The various phases described in the text are denoted by $C$ (cubic $Pm\overline{3}m$), $R_{\mathrm{HT}}$ (rhombohedral $R3m$), $R_{\mathrm{LT}}$ (rhombohedral $R3c$), $T$ (tetragonal $P4mm$), and $M_{\mathrm{A}}$ (monoclinic Cm).

Figure 2

(Color online) Observed and calculated diffraction profiles from the Rietveld refinement of $\mathrm{Pb}{\mathrm{Zr}}_{0.52}{\mathrm{Ti}}_{0.48}{\mathrm{O}}_3$ at $550\mathrm{K}$, with space group $P4mm$. The difference plot is shown below, with short vertical markers denoting the calculated peak positions.

Figure 3

(Color online) Observed and calculated diffraction profiles from the two-phase Rietveld refinement of $\mathrm{Pb}{\mathrm{Zr}}_{0.52}{\mathrm{Ti}}_{0.48}{\mathrm{O}}_3$ at $20\mathrm{K}$, with space groups Cm and Ic. The difference plot is shown below, with upper and lower sets of vertical markers denoting the calculated peak positions for Cm and Ic, respectively. The position of the weak superlattice peak at $2\theta \approx 36.8°$ (pseudocubic $3∕21∕21∕2$) is indicated with an asterisk.

Figure 4

(Color online) Observed and calculated diffraction profiles and difference plots in the region around the strongest superlattice peak from $\mathrm{Pb}{\mathrm{Zr}}_{0.52}{\mathrm{Ti}}_{0.48}{\mathrm{O}}_3$ at $20\mathrm{K}$ for single-phase Ic (left panel), two-phase $Cm+R3c$ (center panel), and two-phase $Cm+\mathit{Ic}$ (right panel).

Figure 5

(Color online) Observed and calculated diffraction profiles and difference plots in the region around the pseudocubic (200) reflection from $\mathrm{Pb}{\mathrm{Zr}}_{0.52}{\mathrm{Ti}}_{0.48}{\mathrm{O}}_3$ at $20\mathrm{K}$ for single-phase Ic (left panel), two-phase $Cm+R3c$ (center panel), and two-phase $Cm+\mathit{Ic}$ (right panel).

Figure 6

(Color online) Observed and calculated diffraction profiles from the three-phase Rietveld refinement of $\mathrm{Pb}{\mathrm{Zr}}_{0.52}{\mathrm{Ti}}_{0.48}{\mathrm{O}}_3$ at $325\mathrm{K}$, with space groups $P4mm$, Cm, and $Pm\overline{3}m$. The difference plot is shown below, with upper, middle, and lower sets of vertical markers denoting the calculated peak positions for $P4mm$, Cm, and $Pm\overline{3}m$ respectively.