Highly transparent ceramics of La‐doped 0.75Pb(Mg1/3Nb2/3)O3–0.25PbTiO3 were fabricated by a two‐stage sintering method from conventional raw materials. The ceramics exhibited a transparency as high as 65% for the infrared wavelength. Large quadratic electro‐optic coefficient of 66 × 10−16 (m/v)2 was obtained, which was the highest value reported so far in Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics. The ferroelectric phase inducing the threshold electric field Eth and the domain structure of the transparent ceramics were studied.

Transparent ceramics of La-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) x/75/25 are prepared, and the ferroelectric domains, dielectric, and ferroelectric properties of x/75/25 are investigated. A double hysteresis loop and small fingerprint domains with uniform distribution observed for 3/75/25 indicate an intermediate ferroelectric state. The dielectric behavior under dc bias and the evolution of the hysteresis loop with increasing electric field for 3/75/25 indicate an electric field-induced phase transition, and it is proposed that the unstable intermediate ferroelectric state which would experience obvious field-induced phase transition is the origin of the giant electro-optic Kerr effect observed in La-doped PMN-PT 3/75/25.

We show that the phase diagram of the ͑001͒ PbMg 1/3 Nb 2/3 O 3 -xPbTiO 3 ͑PMN-xPT͒ ͑x = 0.00, 0.06, 0.13, and 0.24͒ and ͑111͒ PMN-0.24PT lead-magnesium niobate mixed with lead titanate possesses a quasivertical line in the E electric field -T temperature plot, which hardly depends on the field. The existence of this line has been confirmed by independent studies of single crystals grown in different laboratories, by measuring the dielectric permittivity, compliances, and optical transmission, also in different laboratories. A thermal hysteresis inherent to first order phase transitions complicates the phase diagram. The piezoelectric coefficients of the ͑001͒ PMN-xPT ͑x ϭ 0.06 and 0.13͒ have two peaks versus temperature, at finite fields. The first peak is due to the quasivertical phase boundary. The second is in the vicinity of a turning point of the T m ͑E͒ temperature of the dielectric permittivity diffuse maximum. We show that the second peak prevails at reasonable fields, and the piezoelectric coefficients have comparatively large values at this peak, even at small x.

Highly optically transparent ceramics of (1Àx)Pb(Mg 1/3 Nb 2/3 ) O 3 -xPb(Zr 0.53, Ti 0.47 )O 3 (PMN-PZT) were fabricated by a two-stage sintering method without La-modification. The ceramics exhibited high optical transparency (64% at 1500 nm) for visible and near infrared wavelength. The ferroelectric domain and microstructure of PMN-PZT transparent ceramics prepared were also investigated. Fully dense microstructure was observed in all PMN-PZT transparent ceramic samples. Higher PMN containing compositions exhibited pyrochlore phase and relatively lower transparency for near infrared wavelengths. Fine and irregular fingerprint ferroelectric domains were observed in all PMN-PZT compositions except in the PMN-PZT 67/33 composition that had dense microstructure and pure perovskite phase. This PMN-PZT 67/33 composition exhibited the lowest transparency (40% at 1500 nm) with large-scale macrodomain structure.

The dielectric properties, birefringence, domain structure, electrooptic and pyroelectric effects, specific heat and electroacoustic echo have been investigated in Cd2Nb2O7 at successive phase transitions. Physical properties in different phases have been discussed. The thermoactivated reorientations of polarization at the diffuse phase transition temperatures contribute not only to ε, electrooptic and pyroelectric effects, but also influence the electroacoustic echo relaxation time due to the spectral diffusion mechanism.