High electric-field-induced strain of Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals in multilayer actuators

An optimum composition range (29%≤x≤31%) of 〈001〉 oriented (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃(PMNT) crystals was ascertained for multilayer actuator applications, which exhibited high-strain and low-hysteresis behavior. A −1.5 kV/cm negative E-field can be applied to PMNT ferroelectric samples with low hysteresis. Forty layer actuators with individual element sizes of 7×7×0.7 mm³ were fabricated under identical processing conditions using two different materials: (1) single crystal PMNT and (2) commercial PZT-SF ceramics. Under free-load conditions, 48 μm displacements can been achieved in PMNT actuators at electric fields ranging from −1.5 to 10 kV/cm, which is more than twice the displacement of the PZT-SF actuators driven from −10 to 10 kV/cm. Under 4 kg loading, the displacements in PMNT stain actuators are decreased to 42.5 μm.     

Investigation on optical transmission spectra of (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals

The optical transmission spectra from 0.3 to 11 μm of relaxor ferroelectric single crystals (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) were systematically studied at room temperature in this paper. The crystal is transparent between 0.45 and 5.5 μm and becomes completely absorbing around 0.4 μm in near UV region and 10 μm in infrared region. But the wavelength cutoff in near UV is much sharper than the long wavelength cutoff. As compared with other configurations, tetragonal single crystals possess the optimal transmission properties. The optical transmittance in the wavelength region from 0.45 to 5.5 μm is about 70%. The results show that tetragonal PMN-xPT single crystals are promising for a wide range of optical applications. Some discussions about the oxygen-octahedra structure that determines the basic energy level of the crystals are also presented on the optical properties of PMN-xPT single crystals.     

Dependence of high electric-field-induced strain on the composition and orientation of Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals

Electric-field-induced strain behavior of (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMNT) crystals with different orientations and compositions was investigated for use as electromechanical actuators. Crystallographically, high strains with low hysteresis were achieved for 〈001〉 oriented rhombohedral crystals (29%≤x≤31%) near a morphotropic phase boundary, rather than 〈110〉 and 〈111〉. Domain instability could explain inferior strain levels and large hysteresis for 〈110〉 and 〈111〉 oriented crystals. Ultrahigh strain levels up to 1.8% could be achieved for 〈001〉 oriented PMNT crystals, being related to an E-field induced phase transition. −2 kV/cm negative E-field can be applied to PMNT ferroelectric material with low hysteresis. High strain with low hysteresis makes PMNT crystals promising candidates for high performance solid-state actuators.     

Bias field effects on the dielectric properties of 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single crystals with different orientations

The domain states and phase transitions in 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ single crystals were investigated by studying their relative permittivity under various dc bias at constant heating and cooling rates. The orientation dependence of the bias field effect was revealed by examining the temperature dependence of relative permittivity as a function of crystal orientation (the 〈111〉, 〈011〉 and 〈001〉 directions) and dc bias field. The crystals basically have a macrodomain rhombohedral ferroelectric state in the ferroelectric phase under zero dc bias. External bias field could modulate the domain state and induce a stable macrodomain state in the crystals. Also, it is proposed that the dc bias applied along the 〈001〉 or 〈011〉 direction could induce a tetragonal ferroelectric phase or an orthorhombic ferroelectric phase, respectively, in an intermediate temperature range.     

Phase transformation in (0.90−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3-0.10PbZrO3 piezoelectric ceramic: X-ray diffraction and Raman investigation

Piezoelectric ceramics with compositions of (0.90−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃-0.10PbZrO₃, x=0.28, 0.31, 0.34, 0.37, 0.40 and 0.43, were prepared using the conventional columbite precursor method, and their structural phase transformation and piezoelectric behaviors near the morphotropic phase boundary (MPB) have been systematically investigated as a function of PbTiO₃ content. X-ray diffraction (XRD) results demonstrate that the structure of the ceramics experiences a gradual transition process from rhombohedral phase to tetragonal phase with the increasing of PbTiO₃ content, and that compositions with x=0.34-0.40 lie in the MPB region of this ternary system. A Raman spectra investigation of the ceramic samples testified to the transformation process of rhombohedral phase to tetragonal phase by comparing the relative intensities of tetragonal E(2TO₁) mode and rhombohedral phase R_h mode. The structure information was also correlated to the parabola change of the piezoelectric constant; the maximum piezoelectric constants were obtained near the MPB region.     

Electro-optic characterization of tetragonal (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals by a modified Sénarmont setup

The refractive indices of tetragonal (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) single crystals were measured with a prism coupler and their linear electro-optic (EO) properties were investigated from 20 to 80 °C by the automated scanning Sénarmont system with an ac field. The composition and temperature effect on the EO coefficients were also discussed. It has been found that their EO coefficients are much larger than that of widely used LiNbO₃ single crystal and the calculated half-wave voltages are also much lower, which enable the operation at lower voltages and the smaller device dimensions. Since the excellent EO properties are very stable and such high quality single crystals with large-size have been obtained, the PMN-xPT single crystals are a very promising candidate for EO modulation applications. By linking to the polarization-related quadratic EO coefficients, we find that the linear EO properties are related with the spontaneous polarization and dielectric constants.     

Sub-coercive field dynamic hysteresis in morphotropic phase boundary composition of Pb(Zr1/2Ti1/2)O3-Pb(Zn1/3Nb2/3)O3 ceramic and its scaling behavior

Sub-coercive field dynamic ferroelectric hysteresis of a morphotropic phase boundary composition of the PZT-PZN ceramic was investigated under influence of the compressive stress. The scaling relation of hysteresis area 〈A〉 against frequency f, field amplitude E₀, and stress σ took a form of , which is not different significantly to that of other PZT-PZN compositions with pure tetragonal or rhombohedral structure, as well as to that of soft and hard PZT bulk ceramics. This study suggested that the domain structures, not ceramic compositions, played a key role in controlling dynamic hysteresis behavior of ferroelectric materials.     

Epitaxial growth and structural characterization of Pb(Fe1/2Nb1/2)O3 thin films

We have grown lead iron niobate thin films with composition Pb(Fe_1/2Nb_1/2)O₃ (PFN) on (0 0 1) SrTiO₃ substrates by pulsed laser deposition. The influence of the deposition conditions on the phase purity was studied. Due to similar thermodynamic stability spaces, a pyrochlore phase often coexists with the PFN perovskite phase. By optimizing the kinetic parameters, we succeeded in identifying a deposition window which resulted in epitaxial perovskite-phase PFN thin films with no identifiable trace of impurity phases appearing in the X-ray diffractograms. PFN films having thicknesses between 20 and 200 nm were smooth and epitaxially oriented with the substrate and as demonstrated by RHEED streaks which were aligned with the substrate axes. X-ray diffraction showed that the films were completely c-axis oriented and of excellent crystalline quality with low mosaicity (X-ray rocking curve FWHM?0.09°). The surface roughness of thin films was also investigated by atomic force microscopy. The root-mean-square roughness varies between 0.9 nm for 50-nm-thick films to 16 nm for 100-nm-thick films. We also observe a correlation between grain size, surface roughness and film thickness.     

Photoluminescence at room temperature in polycrystalline BaxSr1−xTiO3 ceramics obtained by solid-state reaction method

Stoichiometric Ba_xSr_1−xTiO₃ ceramics (x=0.7, 0.8, and 0.9) have been prepared by solid-state reaction method. It has been observed in our experiments that the photoluminescence (PL) spectra in such samples at room temperature were centered around 800 nm; the results have been found to differ from observations in current literature. An explanation of this phenomenon was given, and the origin of such photoluminescence is ascribed to certain defects existing in these compounds, such as oxygen vacancies.     

Electrical properties of high Curie temperature (1−x)Pb(In1/2Nb1/2)O3-xPbTiO3 single crystals grown by the solution Bridgman technique

0.65Pb(In_1/2Nb_1/2)O₃-0.35PbTiO₃ (PINT65/35) (starting composition) single crystals were grown successfully through the solution Bridgman technique using PbO flux and PMNT67/33 seed crystals. Because of the composition variation, the final composition of achievable crystals is in a range of 0.32-0.34 with the corresponding T_c range of 265-269 °C. The (001) plates of as-grown PINT66/34 single crystals show high Curie temperature (T_c=269 °C) and rhombohedral-tetragonal phase transition temperature (T_rt=134 °C). Besides, good electrical properties with high dielectric constant (ε>3000), low dielectric loss (tan δ∼1.2%), high piezoelectric constant (d₃₃∼2000 pC/N) and large electromechanical coupling factor (k_t≈59%) at room temperature have been obtained on the (001) plates. The sound velocity, acoustic impedance and other piezoelectric parameters were also measured on the (001) plates in this study, which provide us more detailed information about PINT66/34 single crystals.     

Effect of incorporating nonlanthanoidal indium on optical properties of ferroelectric Bi4Ti3O12 thin films

Bi₄Ti₃O₁₂ (BTO) and Bi_3.25In_0.75Ti₃O₁₂ (BTO:In) thin films were prepared on fused quartz and LaNiO₃/Si (LNO) substrates by chemical solution deposition (CSD). Their microstructures, ferroelectric and optical properties were investigated by X-ray diffraction, scanning electron microscope, ferroelectric tester and UV-visible-NIR spectrophotometer, respectively. The optical band-gaps of the films were found to be 3.64 and 3.45 eV for the BTO and BTO:In films, respectively. Optical constants (refractive indexes and extinction coefficients) were determined from the optical transmittance spectra using the envelope method. Following the single electronic oscillator model, the single oscillator energy E₀, the dispersion energy E_d, the average interband oscillator wavelength λ₀, the average oscillator strength S₀, the refractive index dispersion parameter (E₀/S₀), the chemical bonding quantity β, and the long wavelength refractive index n_∞ were obtained and analyzed. Both the refractive index and extinction coefficient of the BTO:In films are smaller than those of the BTO films. Furthermore, the refractive index dispersion parameter (E₀/S₀) increases and the chemical bonding quantity β decreases in the BTO and BTO:In films compared with those of bulk.     

Domain structures in tetragonal Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals studied by piezoresponse force microscopy

The domain structures in (001) surface of Pb(Mg_1/3Nb_2/3)O₃-40% PbTiO₃ single crystals were investigated by piezoresponse force microscopy. Both micron-sized fingerprint 180° and parallel 90° domains were observed in the sample. Different sets of favourable {110} oriented domain patterns were found to meet, intersect or grow through each other. In addition, the piezoelectricity decreases sharply at the domain walls in 180° structures, but does not in the 90° domain structures.     

Photoluminescence investigations of Zn2SiO4 co-doped with Eu and Tb ions

Zinc silicate phosphors co-doped with Eu³⁺ ions and also with both Eu³⁺ and Tb³⁺ ions were prepared by high temperature solid state reaction in air or reducing atmosphere. The luminescence characteristics of the prepared phosphors were investigated. While in the samples prepared in air, Eu³⁺ emission was found to be dominant over Tb³⁺ emission, in the samples prepared in reducing atmosphere, intense Eu²⁺ emission at 448 nm was found to be predominant over narrow Tb³⁺ emission. Luminescence studies showed that Eu³⁺ ions occupy asymmetric sites in Zn₂SiO₄ lattice. The intense f-f absorption peak of Eu³⁺ at 395 nm observed in these phosphors suggests their potential as red emitting phosphors for near ultra-violet light emitting diodes.     

Ce and Pr5d-energy levels in the (pseudo) perovskites KMgF3 and NaMgF3

The location of the 5d-energy levels of Ce³⁺ and Pr³⁺ in the cubic perovskite KMgF₃ and in the distorted perovskite NaMgF₃ was determined from spectroscopic studies in the vacuum ultraviolet. It is established that Ce³⁺ and Pr³⁺ ions both occupy the same site in each host: K⁺ sites for KMgF₃ and Na⁺ sites for NaMgF₃. The small crystal field splitting and the small value of the centroid shift of the 4fⁿ⁻¹5d-configuration yield a relatively high energy for the lowest 5d state of both Ce³⁺ and Pr³⁺. The lowest 5d state of Pr³⁺ in both hosts is found at energy higher than the 4f² state, enabling the photon cascade emission to occur.     

Influence of niobium doping on the electrical properties of 0.58Pb(Sc1/2Nb1/2)O3-0.42PbTiO3 single crystal

Piezoelectric single crystals of 0.58Pb(Sc_1/2Nb_1/2)-0.42PbTiO₃ and Nb⁵⁺-doped PSN-PT have been grown using flux technique. It is believed that the addition of Nb⁵⁺ creates lead vacancy in order to compensate charge neutrality. The structural distortion that occured in the doped crystals has been revealed through broadening of some peaks in X-ray diffraction studies. Niobium content that increased from 0.50 to 1.00 mol% might have induced more defect dipoles associated with . This plays a significant role in improving the ferroelectric, dielectric and piezoelectric properties. Our observations clearly show an increase in the spontaneous polarization (P_r), dielectric constant at room temperature, degree of diffuseness and transition temperature (T_c) and also a decrease in coercive field. The reasons behind these enhanced electrical properties are discussed in detail.     

Double-hysteresis-like loops in Mn-doped (Pb,La)(Zr,Ti)O3 ceramics

PLZT12/40/60 ceramics doped with different Mn content were prepared by a conventional mixed oxide method. The shrinkage of some local crystal cells was confirmed by XRD diffraction. The effect of Mn doping on the hysteresis loop was investigated. A peculiar double-hysteresis-like loop was found and various possible mechanisms were discussed. Random local strains caused by shrunk crystal cells can satisfactorily explain the double hysteresis characteristics. The dependence of the double-hysteresis-like loops on temperature was also investigated. Due to the heat activation of polar moments in shrunk crystal cells, the double-hysteresis-like loops can transform into a normal one when the temperature is rising.     

Photoluminescence in amorphous (PbLa)TiO3 thin films deposited on different substrates

Pb_1−XLa_XTiO₃ thin films, (X=0.0; 13 and 0.27 mol%) were prepared by the polymeric precursor method. Thin films were deposited on Pt/Ti/SiO₂/Si (1 1 1), Si (1 0 0) and glass substrates by spin coating, and annealed in the 200-300°C range in an O₂ atmosphere. X-ray diffraction, scanning electron microscopy and atomic force microscopy were used for the microstructural characterization of the thin films. Photoluminescence (PL) at room temperature has been observed in thin films of (PbLa)TiO₃. The films deposited on Pt/Ti/SiO₂/Si substrates present PL intensity greater than those deposited on glass and silicon substrates. The intensity of PL in these thin films was found to be dependent on the thermal treatment and lanthanum molar concentration.     

Unusual luminescence of octahedrally coordinated divalent europium ion in Cs2MP2O7 (M=Ca, Sr)

The excitation and emission spectra of octahedrally coordinated europium ion (Eu²⁺) ions in Cs₂M²⁺P₂O₇ (M²⁺=Ca, Sr) are reported and discussed. The remarkable features of the Eu²⁺ luminescence in these phosphate materials include (a) very large Stokes shift of emission (∼1 eV), (b) high luminescence quenching temperature, and (c) unusually low energy of the emitted photons for Eu²⁺ luminescence in phosphate-based materials. The broad emission bands of Eu²⁺ in Cs₂CaP₂O₇ and Cs₂SrP₂O₇ peak at 607 and 563 nm, respectively. The Stokes shift, crystal field splitting, centroid shift and the red shift of the Eu²⁺ 4f⁶5d¹ electronic configuration have been estimated from the relevant optical data. The radiative lifetime of the Eu²⁺ emission in Cs₂M²⁺P₂O₇ is ∼1.2 μs. The nature of the Eu²⁺ emission in Cs₂M²⁺P₂O₇ is discussed and arguments are presented to associate the luminescence with an extreme case of normal 4f⁶5d¹→4f⁷[⁸S_7/2] emission.     

Phase transition, structural and electrical properties of Pb(Zn1/3Nb2/3)O3-doped Pb(Ni1/3Nb2/3)O3-PbTiO3 ceramics prepared by solid-state reaction method

Phase pure perovskite (1−x−y)Pb(Ni_1/3Nb_2/3)O₃-xPb(Zn_1/3Nb_2/3)O₃-yPbTiO₃ (PNN-PZN-PT) ferroelectric ceramics were prepared by conventional solid-state reaction method via a B-site oxide mixing route. The PNN-PZN-PT ceramics sintered at the optimized condition of 1185 °C for 2 h exhibit high relative density and rather homogenous microstructure. With the increase of PbTiO₃ (PT) content, crystal structure and electrical properties of the synthesized PNN-PZN-PT ceramics exhibit successive phase transformation. A morphotropic phase boundary (MPB) is supposed to form in (0.9−x)PNN-0.1PZN-xPT at a region of x=32-36 mol% confirmed by X-ray diffraction (XRD) measurement and dielectric measurement. The MPB composition can be pictured as providing a “bridge” connecting rhombohedral ferroelectric (FE) phase and tetragonal one since crystal structure of the MPB composition is similar to both the rhombohedral and tetragonal lattices. Dielectric response of the sintered PNN-PZN-PT ceramics also exhibits successive phase-transition character. 0.64PNN-0.1PZN-0.26PT exhibits broad, diffused and frequency dependent dielectric peaks indicating a character of diffused FE-paraelectric (PE) phase transition of relaxor ferroelectrics and 0.40PNN-0.1PZN-0.50PT exhibits narrow, sharp and frequency independent dielectric peaks indicating a character of first-order FE-PE phase transition of normal ferroelectrics. The FE-PE phase transition of 0.56PNN-0.1PZN-0.34PT is nearly first-order with some diffused character, which also exhibits the largest value of piezoelectric constant d₃₃ of 462pC/N.