The crystal structure of antiferroeletric $Pb(Yb_{1/2}Nb_{1/2})O_3$ has been characterized. Both X-ray diffraction and transmission electron diffraction show two sets of supperlattice refrections originating respectively form the B-site atom ordering and the antiparallel lead-atom displacement, which suffer within the orthorhombic $a_0-b_0$ plane along the $a_0$-direction. The room temperature crystal symmetry is considered to be orthorhombic with space group Pbnm$(D_2h16)$ and lattice parameters $a_0$=5.918Å, $b_0$=23.453Å, and $c_0$=8.221Å. The phase relationships between orhorhombic superlattice and momoclinic sublattice are given by $a_o=(a_c+b_c), b_o=4(-a_c+b_c)$ and $c_o=2c_c$. High-resolution electron microscopy confirms the diffaction results.
Dielectric, X-ray diffraction, calorimetric and dilatometric measurements were used to characterize the structural phase transition occuring in antiferroelectric $Pb(Yb_{1/2}Nb_{1/2})O_3$ compound. Dielectric behavior for ceramics shows a sharp transition with a large temperature hysteresis near antiferroelectric-paraelectric transition temperature 302℃. Lattice parameters and spontaneous strain have been investigated between 20 and 400℃ using X-ray powder diffraction. High temperature X-ray results indicate that the structural phase transition from the lower-symmetry phase (Pbnm) to the cubic paraelectric phase(Fm3m($O_h^5$)) occurs at about 302℃ on heating. The temperatrue dependence of the spontaneous strain is discussed by phenomenological theory of antiferroelectricity. Non-obserbable antiferroelectric polarization in $Pb((Yb_{1/2}Nb_{1/2})O_3$ is respectively estimated as 0.327 and 0.207coul/㎡ at 20 and 302℃ from the $Q_hC$(=$3.1\pm 0.4\times 10^3m^4$, $coul^{-2}K$) constant rule and the transition entropy change(ΔS) measurement.
A phase analysis in antiferroelectric-ferroelectric solid solution system(1-x) $Pb(Yb_{1/2}Nb_{1/2})O_3-(X)Pb(Fe_{1/2}Nb_{1/2})O_3$ has been conducted by its crystallographic, dielectric, calorimetric and dilatometric measurements. The system is founded to form a solid solution of the perovskite structure through the entire composition range. The character of its phase transition can be classified by three distinct types depending on composition x.
For the composition range of 0.0≤x<0.13, its low temperature phase is determined as orthorhombic-antiferro-electric. Its sublattice symmetry is monoclinic. The transition from the antiferroelectric to the paraelectric phase is relatively sharp and of first order in nature, which are supported by the volume discontinuity and large dielectric thermal hysteresis change observed near transition temperatrue. With increasing $Pb(Fe_{1/2}Nb_{1/2})O_3$ content(x) in 0.0≤x<0.13, the transition temperature(Tc), reflection intensity due to antiparallel dipole ordering and degree of B-site order decrease relatively. This result suggests that the substitutional $Pb(Fe_{1/2}Nb_{1/2})O_3$ acts as hard component depressing antiferroelectric-paraelectric transition of $Pb(Yb_{1/2}Nb_{1/2})O_3$.
For 0.13
