Fabrication and properties of PLT/PLZT/PLT structures obtained by RF magnetron sputtering

Ferroelectric Pb_0.84La_0.16Ti_0.96O₃/Pb_0.96La_0.04(Zr_0.52Ti_0.48)_0.99O₃/Pb_0.84La_0.16Ti_0.96O₃ (PLT/PLZT/PLT) structures were fabricated on platinum-coated silicon wafers by RF magnetron sputtering. A Pb_0.84La_0.16Ti_0.96O₃ layer was used as a seed layer to improve the crystallization and enhance the ferroelectric properties of the PLZT film. With the PLT seed layers, the films showed excellent ferroelectric properties in terms of large remnant polarization (2P_r) of 52.7 μC/cm², lower coercive field (2E_c) of 130 kV/cm for an applied field of 500 kV/cm. Moreover, the PLT/PLZT/PLT structures exhibited good fatigue endurance after 10¹⁰ switching cycles, which was attributed to the double-sided PLT layers. They improved the electrical fatigue by eliminating the pyrochlore phase, reduced the strong (111) orientation, and assimilated the oxygen vacancies from the PLZT layer.     

Defects induced by electron irradiation in hollandite ceramics, specific radioactive cesium-host wasteforms: a 57Fe Mössbauer study

Several single phase hollandite ceramics having Ba²⁺ _x Cs⁺ _y (C = Al,Fe)³⁺ _2x+y Ti⁴⁺ _8?2x?y O₁₆ composition have been synthesized and irradiated under external electron beams simulating the β-irradiation of radioactive cesium. These samples have been characterized by ⁵⁷Fe transmission Mössbauer spectroscopy. Mössbauer results show that the irradiation modifies the local arrangements of Ba cations around Fe³⁺ ions by atomic displacement of Ba ions.     

Experimental evidence of breakdown strength and its effect on energy-storage performance in normal and relaxor ferroelectric films

Normal-ferroelectric Pb(Zr_0.52Ti_0.48)O₃ (PZT) and relaxor-ferroelectric Pb_0.9La_0.1(Zr_0.52Ti_0.48)O₃ (PLZT) thin-films are deposited on SrRuO₃-covered SrTiO₃/Si substrates. An ultrahigh recoverable energy-storage density (U_reco) of 68.2 J/cm³ and energy efficiency (η) of 80.4% are achieved in the PLZT thin-films under a large breakdown strength (E_BD) of 3600 kV/cm. These values are much lower in the PZT thin-films (U_reco of 10.3 J/cm³ and η of 62.4% at E_BD of 1000 kV/cm). In addition, the remanent polarization (P_r) and dielectric-constant are also investigated to evaluate the breakdown strength in thin-films. Polar nano-regions (PNRs) are created in the PLZT thin-films to enable relaxor behavior and lead to slim polarization loops along with very small P_r. The excellent operating temperature of energy-storage performance and also the breakdown strength obtained in the PLZT thin-films are mainly ascribed to the presence of PNRs. Moreover, both PZT and PLZT thin-films exhibit superior performance up to 10¹⁰ times of charge-discharge cycling.     

ESR and optical spectroscopy of copper-doped PLZT electro-optic ceramics

2+ spectra in axial and cubic crystal fields. Cu²⁺ substitutes for Ti⁴⁺ and the excess charge can be compensated by La³⁺ on a nearest-neighbor site, thus creating axial symmetry. The centers of cubic symmetry are those where the charge is compensated in distant spheres. In contrast to pure PLZT, PLZT:Cu exhibits a new luminescence band peaking at 1.18 eV. This emission is ascribed to the ²T₂(D)→²E(D) transition of Cu²⁺(3d⁹) which can be excited either in the resonant 1.87 eV band or via charge-transfer excitation bands at 2.40, 2.57, and 3.03 eV. The absorption band at 1.45 eV is assumed to be that of Cu⁺ ions. Annealing in hydrogen and in oxygen atmospheres caused decrease and restoration, respectively, of the ESR and luminescence intensities as a consequence of Cu²⁺ conversion into Cu¹⁺ and vice versa. Received: 14 November 1997/Accepted: 8 December 1997     

Magnetic resonance in Pb<Subscript>x</Subscript>Nb<Subscript>y</Subscript>O<Subscript>z</Subscript> ceramics as a system containing chemical fluctuation regions

Simulation of the chemical fluctuation regions in PMN-like relaxors through growth of the Pb_xNb_yO_z eramics was performed. Different Pb_xNb_yO_z clusters (chemically and structurally) coexist in such ceramics. Hole polaron and bipolaron (Cr³⁺-two polaronic-hole) paramagnetic complexes were considered for explanation of the EPR spectra in Pb_xNb_yO_z ceramics. Dynamical averaging, light-induced effects, and significant effects of reduction treatment giving the coexistence of Nb⁵⁺ and Nb³⁺ ions, as well as of a strong internal magnetic field, were discovered in this ceramics. The latter could be related to antiferromagnetic phase realization in Pb_xNb_yO_z clusters containing a sufficiently high concentration of magnetic Nb³⁺ host lattice ions. Such a situation leads to antiferromagnetic resonance on Nb³⁺ ions, as well as to EPR of Cr³⁺-related paramagnetic complexes in a Nb³⁺-induced internal magnetic field. Charge transfer vibronic excitons (CTVE) in free and in CTVE phase states were detected in Pb_xNb_yO_z ceramics by photoluminescence studies.     

Optical properties of Er/Yb-codoped transparent PLZT ceramic

Optical absorption and emission spectra of Er³⁺/Yb³⁺ ions in PLZT (Pb_1−xLa_xZr_yTi_1−yO₃) ceramic have been studied. Based on the Judd—Ofelt (J-O) theory, the J-O intensity parameters were calculated to be Ω₂=2.021×10⁻²⁰ cm², Ω₄=0.423×10⁻²⁰ cm², Ω₆=0.051×10⁻²⁰ cm² from the absorption spectrum of Er³⁺/Yb³⁺-codoped PLZT. The J-O intensity parameters have been used to calculate the radiative lifetimes and the branching ratios for some excited ⁴I_13/2, ⁴I_11/2, ⁴I_9/2⁴F_9/2, and ⁴S_3/2 levels of Er³⁺ ion. The stimulated emission cross-section (8.24×10⁻²¹ cm²) was evaluated for the ⁴I_13/2→⁴I_15/2 transition of Er³⁺. The upconversion emissions at 538, 564, and 666 nm have been observed in Er³⁺/Yb³⁺-codoped PLZT by exciting at 980 nm, and their origins were identified and analyzed.     

Dielectric, ferroelectric and pyroelectric properties of Pb[(Ni1/3Sb2/3)xTiyZrz]O3 ceramics

In the present study, various Pb[(Ni_1/3Sb_2/3)_xTi_yZr_z]O₃ where x+y+z=1, x=0.08 and y=0.44-0.49, ceramics in the morphotropic phase boundary (MPB) range were studied by dielectric and pyroelectric methods. The results of the investigations revealed an MPB composition range of y≅0.46. The study of the dielectric properties of these compounds as a function of temperature suggests that with increase in y the permittivity maximum increases and transition temperature shifts towards higher temperature. Well-saturated polarization versus electric field (P-E) hysteresis loops were obtained and values of P_r were calculated. The samples revealed good pyroelectric properties for y=0.44 and y=0.45 at room temperature with large figures of merit F_v=0.019 m²/C and F_D=1.34×10^-5Pa^1/2.     

Photoinduced centers in the optically transparent ceramic PLZT 8/65/35

The photoinduced centers in the nominally pure, optically transparent ceramic PLZT 8/65/35 and samples doped with Cu, Mn, Fe, and Co (0.1 and 0.01%) are investigated by ESR at 24 K. Photoinduced ESR signals are observed with g _eff=1.995 and 1.94, caused by Pb³⁺ and Ti³⁺ ions, respectively, and with g _eff=2.015, which can be assigned to an F center, i.e., an electron in an oxygen vacancy. The influence of heating and doping of the samples on the intensity of the ESR signals is studied. An analysis of the results obtained corroborates models of the photoinduced centers and a scheme of their local electronic levels. Fiz. Tverd. Tela (St. Petersburg) 39, 1833–1837 (October 1997)     

Substrate and orientation influence on electrical properties of sputtered La-doped PZT thin films

Pb_1−2y/3La_yZr_xTi_1−xO₃ (PLZT) thin films have been prepared “in situ” by multi-target sputtering on Silicon, LaAlO₃ (LAO) and MgO substrates covered with a Pt bottom electrode. The purpose was to grow tetragonal PLZT films (Zr/Ti = 28/72 with different La contents) on these various substrates and to compare their electrical properties. To this aim, Pt was first deposited on the three different substrates to get (1 1 1)Pt/Si, (1 1 1)Pt/LAO and (2 0 0)Pt/MgO. Then PLZT was deposited in a same run on these three kinds of substrates and the influence of La contents and film orientation on electrical properties was investigated. The La content was varied from y = 0 to y = 32 in order to explore the phase transition between ferroelectric and paraelectric phases as a function of the substrate. For large amount of Lanthanum, relaxor behavior has been observed and studied.     

Synthesis and ionic conduction of C3A-type nasicon Na3+3x−yY1−xSi3−yPyO9

In the solid solutions of Na_3+3x−yY_1−xSi_3−yP_yO₉, new fast Na⁺ -conductors were obtained. The ionic conductivity, σ, and the activation energy, E, of the most conductive material, Na_4.425Y_0.375Si_2.55P_0.45O₉ were 5 × 10⁻³ S/cm at 300°C and 10 kcal/mol, respectively. Those values were strongly dependent upon the composition. With an increase of Na concentration, [Na], σ increased and E decreased. Accommodation of higher [Na] in the structure was madefeasible by decreasing [Y] and increasing [P]. Based on the crystal structure assumed for Na_3+3x−yY_1−xSi_3−yP_yO₉ and on the above results, a conduction model was presented. The structural consideration revealed that a conduction path is formed along the 〈1 1 1 〉 direction, where Y³⁺ ions locate in the way of Na⁺ ions.     

Microstructure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–LiNbO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of (1?x?y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yLiNbO₃ (BNT–BKT–LN-x/y) have been fabricated by a conventional solid-state reaction method, and their microstructure and electrical properties have been investigated. The results of X-ray diffraction (XRD) measurement show that K⁺, Li⁺ and Nb⁵⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a solid solution with a pure perovskite structure. The BKT and LN addition has no remarkable effect on the crystal structure. However, a significant change in grain size took place. Simultaneously, with increasing amount of LN, the temperature for a ferroelectric–antiferroelectric phase transition is clearly reduced. The temperature dependence of dielectric properties suggests that the ceramics have diffuse-type phase transition characteristics. The piezoelectric constant d₃₃ and the electromechanical coupling factor k_p of the ceramics attain maximum values of 195 pC/N and 0.336 at x=0.18 and y=0.01.     

Ferroelectric and pyroelectric properties of Ce3+ modified tetragonal tungsten bronze structured lead barium niobate-55 ceramics

In this work, Lead Barium Niobate-55 tetragonal tungsten bronze structured ceramics modified with Ce³⁺ with the stoichiometric formula Pb_0.55?(3y/2)Ce_yBa_0.45Nb₂O₆, where y=0–10 mol% Ce³⁺, were fabricated through the solid state reaction method and investigated for ferroelectric and pyroelectric properties. Pb_0.55?(3y/2)Ce_yBa_0.45Nb₂O₆ (PBN55) exhibited tetragonal (4mm) tungsten bronze structure. The ferroelectric properties (spontaneous polarization, P_s, remanent polarization, P_r and coercive field, E_c), as a function of Ce³⁺ concentration, have been reported. The influence of Ce³⁺ on pyroelectric properties of the PBN55 system has been evaluated. The pyroelectric properties were characterized and discussed as a function of Ce³⁺. The 6 mol% Ce³⁺ modified tetragonal PBN55 composition exhibited optimum pyroelectric properties in the series which could be suitable for possible pyroelectric applications.     

Dynamics of birefringence properties in 17/30/70 PLZT ceramics

Birefringent properties of PLZT ceramics (Pb₈₃La₁₇)(Zr₃₀Ti₇₀)O₃ were investigated by measuring the transverse electrooptic effect in a 0.2 mm-thick wafer at various speeds of external voltage changes. At least two types of internal polarized microregions of different physical nature in charge of the electrooptical properties are observed.     

Effect of Cu-stoichiometry on the dielectric and electric properties in CaCu3Ti4O12 ceramics

CaCu_3+yTi₄O₁₂ (y=0, ±0.025, ±0.05, ±0.1 and −0.15) ceramics are prepared by the conventional solid-state reaction technique under sintering condition of 1050 ^°C, 10 h. X-ray diffraction shows that they all have the good crystalline structure. Cu-deficient ceramics exhibit the microstructures of uniform grain size distribution, whereas both Cu-stoichiometric and Cu-rich ceramics display microstructures of bimodal grain size distribution. The largeness of low-frequency dielectric permittivity at room temperature is found to be very sensitive to the Cu-stoichiometry. Upon raising the measuring temperature, all of the ceramics present commonly three semicircles in the complex impedance plane. It indicates that there exist three distinct contributions, which are ascribed to arising from domains, grain boundaries and domain boundaries. In addition, the influence of CuO segregation on the dielectric and electrical properties is also discussed.     

Structural and dielectric properties of phosphorous-doped PLZT ceramics

In the present work we have reported the unique effects of P₂O₅-doped PLZT ceramics with composition (Pb_0.92La_0.08)(Zr_0.65Ti_0.35)O₃ +x wt% of P₂O₅ (wherex = 1, 3 and 5) prepared chemically by co-precipitation method. X-ray diffraction studies suggest that the prepared compound was very fine (10–25 nm), homogeneous and of rhombohedral symmetry. The apparent density of samples decreased with the P⁵⁺ additions. Studies of dielectric constant and dielectric loss as a function of frequency (10–1000 kHz) and temperature suggest that the compound undergoes diffuse type of phase transition without any sign of relaxor behaviour. With increasingx, dielectric constant was found to decrease appreciably, whereas Curie temperature (T_C) was found to increase     

Electrooptical properties and photoinduced effects in plzt ceramics applications to optical storage and processing of information

After defining the properties of transparent lead-lanthanum zirconate-titanate ceramics (PLZT) we report the results of holographic and digital recording in quadratic electrooptic ceramics Pb_0.91La_0.09(Zr_0.65Ti_0.35)_0.9775O₃. Photoinduced refractive index changes in these ceramics by deflected and modulated argon laser beams, the behaviour of the diffraction efficiency versus light power density and applied field, the possibility of image selection and optical selective erasure are explained phenomenologically in terms of a photoinduced field model.     

二价Ba2+、Pb2+和四价Ti4+在硼硅酸盐玻璃系统中对Li+/Na+离子交换的影响

本文讨论了在硼硅酸盐玻璃系统中引入二价Ba²⁺、Pb²⁺和四价Ti⁴⁺后,由于Pb²⁺和Ti⁴⁺配位结构的变化,引起Pb²⁺、Ti⁴⁺场强及其与O^2-离子间距的变化,对Li⁺/Na⁺离子交换产生影响,从而改变折射率差值(ΔN)和折射率分布.     

Electrical properties of neodymium doped CaBi4Ti4O15 ceramics

Neodymium doped bismuth layer structure ferroelectrics (BLSFs) ceramics CaBi_4−xNd_xTi₄O₁₅ (x=0, 0.25, 0.50, 0.75) were prepared by solid-state reaction method. X-ray diffraction pattern showed that single phase was formed when x=0-0.75. The refined lattice parameters showed that a (b) axes decrease at x=0.25 and increase with more Nd³⁺ dopant. The effects of Nd³⁺ doping on the dielectric and ferroelectric properties of CaBi₄Ti₄O₁₅ ceramics are studied. Nd³⁺ dopant decreased the Curie temperature linearly, and the dielectric loss, tan δ, as well. The remnant polarization of Nd³⁺ doped CaBi₄Ti₄O₁₅ ceramics was increased by 80% at x=0.25, while more Nd³⁺ dopant decreased the remnant polarization. CaBi_3.75Nd_0.25Ti₄O₁₅ ceramics had the largest piezoelectric constant d₃₃. The structure and properties of CaBi_4−xNd_xTi₄O₁₅ ceramics showed that Nd³⁺ may occupy different crystal locations when Nd³⁺ content x is less than 0.25 and more than 0.50.     

Preparation and characterization of cerium oxide doped TiO2 nanoparticles

A mixed oxide consisting of TiO₂ as the major phase and CeO_2−y (0<y<0.5) as the dopant phase was prepared via the sol-gel reaction of Ti(i-OC₃H₇)₃ in an aqueous solution of Ce(NO₃)₃. The resulting oxide powders with different CeO_2−y contents were all composed of nano-sized spheres. The CeO_2−y phase was identified to have retarding effect on the phase transition from anatase TiO₂ to rutile TiO₂ at calcinations temperature as high as 800 °C, which would otherwise be a thorough conversion. The CeO_2−y-TiO₂ powders could apparently shift the UV-absorption band of TiO₂ toward visible range, and there was an optimal CeO_2−y content in association with the maximum absorbance. This effect is interpreted as the existence of an n-type impurity band, due to the substitution of Ti⁴⁺ for Ce^3+/4+ at the interface between the two oxides, in the gap of TiO₂. According to X-ray photoelectron spectroscopy (XPS) investigation, the Ti element mainly existed as the chemical state of Ti⁴⁺ and the Ce oxide doping did not affect the peak position of Ti 2p. The Ce 3d spectrum of CeO_2−y-doped TiO₂ sample basically denotes a mixture of Ce^3+/4+ oxidation states giving rise to a myriad of peaks.