A Raman and dielectric study of ferroelectric ceramics

Dielectric and Raman scattering experiments were performed on various ceramics with composition Ba(Ti_1-xZr_x)O₃. Such lead-free, environmental-friendly materials were shown, from dielectric measurements, to exhibit behaviours extending from conventional to relaxor ferroelectrics on increasing the zirconium concentration. The evolution of the Raman spectra was studied as a function of temperature for various compositions, and the spectroscopic signature of the corresponding phases was determined. In the relaxor state, the variation of the integrated intensity of the Raman lines with temperature showed a plateau at low temperature. This anomaly was also detected as a peak in depolarization current measurements, and attributed to ergodicity breaking which characterizes usual relaxor systems. Raman results hint at locally rhombohedral polar nanoregions resulting from the random fields associated with Zr ions. Received 25 September 1998     

Giant dielectric constant observed in Ba0.96Sr0.04Zrx Y0.005Ti0.995–xO3–δ ceramics

Ba_0.96Sr_0.04Zr_x Y_0.005Ti_0.995–xO_3–δ ceramics were prepared by conventional sintering. The dielectric properties and the Curie temperature of the ceramics were studied. The Ba_0.96Sr_0.04Zr_x Y_0.005Ti_0.995–xO_3–δ ceramics (x = 0.04) exhibit a giant dielectric constant (ε_r ～ 10⁵). The peak value of dielectric constant is ～250,000 at 100 Hz and ～70,000 at 1 MHz for Ba_0.96Sr_0.04Zr_x Y_0.005Ti_0.995–xO_3–δ ceramics (x = 0.04). The results show that Ba_0.96Sr_0.04Zr_x Y_0.005Ti_0.995–xO_3–δ (x = 0.04) ceramics are a promising candidate material for microelectronic applications. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ferroelectric-relaxor behavior of (Na0.5K0.5)NbO3-based ceramics

We report that ferroelectric-relaxor behavior is induced by doping of SrO and TiO₂, or BaO and TiO₂ into classic ferroelectric (Na_0.5K_0.5)NbO₃. It is found that [(Na_0.5K_0.5)_0.9Sr_0.1](Nb_0.9Ti_0.1)O₃ ceramics exhibit a pronounced ferroelectric-relaxor behavior, comparable to that of [(Na_0.5K_0.5)_0.9Ba_0.1](Nb_0.9Ti_0.1)O₃ ceramics. Our results indicate that the relaxor behavior is closely related to the appearance of micropolar regions in these systems. The relaxor behavior should arise from the dynamic response of micropolar clusters. Raman spectra of [(Na_0.5K_0.5)_1−xSr_x](Nb_1−xTi_x)O₃ ceramics measured in the wavenumber range from 100 to 1200 cm⁻¹ confirm that the first order scattering is dominant in phonon bands should result from both short-range ordered region (micropolar regions) and disordered matrix. The frequency dependence of dielectric permittivity measurements show that the relaxor behavior of SrO and TiO₂, or BaO and TiO₂ doped (Na_0.5K_0.5)NbO₃ ceramics is not a Debye type in the radio frequency range.     

Investigation of local structure of lead‐free relaxor Ba(Ti0.70Sn0.30)O3 by Raman spectroscopy

The local structure of Ba(Ti_0.70,Sn_0.30)O₃ (BSnT) was investigated using micro Raman spectroscopy from 80 to 500 K, which indicated three local phase sequences. The dielectric spectroscopy studies illustrated freezing of polar nano‐regions (PNR) below 95 K, merger of frequency dispersion at 220 K, and the origin of polar nano‐regions at 482 K. The temperature evolution of Raman spectra, basically integrated intensity, indicates non‐ergodic relaxor phase below 100 K, mature ergodic phase between 100 and 200 K, and the existence of ergodic polar clusters until 450 K, and above paraelectric phase. The observation of local phase sequences by Raman spectra are in agreement with dielectric spectroscopy anomalies. Copyright © 2008 John Wiley & Sons, Ltd.     

Temperature and induced electric field dependence on the phase transition of 9/70/30, 9/65/35 and 9/60/40 PLZT ceramics

In this work, Pb_0.91La_0.09(Zr_1–xTi_x)_0.9775O₃ ceramics where x = 0.3, 0.35 and 0.4 (the composition near MPB) were prepared by solid solution method. After fabrication process, electrical property was measured by LCR meter. Polarization and induced strain behavior of the samples were investigated by using interferometry technique modified with Sawyer–Tower circuit at various temperatures. The results of dielectric, polarization and induced strain properties were due to the Zr/Ti ratios, which changed their behavior when temperature was varied (30–70 °C). The normal to macro-micro domains to relaxor and paraelectric phase transition was demonstrated which is related to linear or nonlinear increase of polarization and induced strain as a function of applied subswitching electric field.     

Crossover from ferroelectric to relaxor behavior in BaTi1− x Sn x O3 solid solutions

Dielectric relaxation of BaTi_{1? x} Sn _x O₃ ceramics is investigated by means of dielectric spectroscopy. The gradual crossover from ferroelectric to relaxor behavior is characterized by vanishing of the contribution due to domain walls and appearance of relaxation related to reorientation of polar nanosized regions. Typical behavior of relaxors is observed only in ceramics with x = 0.30, while the compositions with 0.175 ≤ x ≤ 0.25 show coexistence of both ferroelectric and relaxor features. The relaxor properties are supposed to be due to both weak random fields and disorder inherent in pure BaTiO₃.     

锰掺杂对Ba(Zr,Ti)O3陶瓷压电与介电性能的影响

采用氧化物固相反应法制备了锰掺杂改性的Ba(Zr_0.06Ti_0.94)O₃陶瓷.研究了锰的掺杂量对Ba(Zr_0.06Ti_0.94)Mn_xO₃ (BZTM)陶瓷的结构、介电和压电性能的影响.实验发现,当锰含量x<0.5 mol%时进入晶格,使材料压电性能提高,损耗减小,表现出受主掺杂的特性;当锰含量x>0.5 mo 关键词： Ba(Zr 3 陶瓷')" href="#">Ti)O₃ 陶瓷 锰掺杂 介电性能 压电性能     

Synthesis and Raman investigation of sol–gel‐derived relaxor ferroelectric thin films

Pb(Fe_2/3W_1/3)O₃ (PFW) thin films were deposited on platinized silicon substrate by a chemical solution deposition technique. Room‐temperature X‐ray diffraction (XRD) revealed a pure cubic crystal structure of the investigated material. The microstructure indicated good homogeneity and density of the thin films. A Raman spectroscopic study was carried out on PFW to study the polar nano‐regions in the temperature range 85–300 K. The Raman spectra showed a change in the peak intensity and a shift towards the lower wavenumber side with temperature. The Raman spectra also revealed the transition from the relaxor to the paraelectric state of PFW. There was no evidence of a soft mode in the low‐temperature region, in contrast to the normal ferroelectric behavior. The polar nano‐regions tend to grow and join at low temperatures (∼85 K), which become smaller with increase in temperature. The presence of strong Raman spectra in the cubic phase of the material is due to the presence of distributed Fm3m(Z = 2) symmetry nano‐ordered regions in the Pm3m(Z = 1) cubic phase. Copyright © 2007 John Wiley & Sons, Ltd.     

Structural stability,phase transition and dielectric properties of Pb(Mg1/2W1/2)1−xMxO3 (M = Zr,Sn, Ti) ceramics

ABSTRACT

Pb(Mg_1/2W_1/2)_1?xM_xO₃ (M?=?Zr,Sn,Ti) ceramics have been prepared by the conventional ceramic process. Their crystallographic, phase transition and dielectric properties have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance analyzer in this paper. The solubility of the tetra-valent cation in Pb(Mg_1/2W_1/2)_1?xM_xO₃ decreases in the sequence of Ti^4+?>?Zr^4+?>?Sn⁴⁺. The doping led to the phase transition from orthorhombic antiferroelectric to cubic paraelectric phase, the microscopic nature of which could be attributed to the contraction of Pb-O₁₂ dodecahedron. A definition of the ordering parameter of the cubic phase was deduced to quantitatively evaluate the B-site ordering degree which decreased with the increase in doping concentration. Anti-site disordering of Mg²⁺ and W⁶⁺ occurred in the high-level doping compositions, which led to the relaxor behavior observed in Ti⁴⁺-doped series with x?=?0.01 composition. Both of the maximum dielectric permittivity and loss in the paraelectric phase increased with the increasing doping concentration.     

The piezoelectric effect in Pb[(Fe1/3Sb2/3) x Ti y Zr z ]O3 ceramics

The piezoelectric properties of Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃ with x + y + z = 1, x = 0.1, y = 0.43–0.48 ceramics have been investigated over a broad temperature range using a resonance technique. The influence of modification of PZT normal ferroelectric synthesized near the morphotropic phase boundary by a relaxor Pb(Fe_1/3Sb_2/3)O₃ compound on its physical properties was studied. The coefficients s ₁₁, k ₃₁, and d ₃₁ were calculated from the parameters characterizing the behavior of damped harmonic oscillator in the vicinity of the piezoelectric resonance. Several anomalies of the piezoelectric coefficients have been found in the temperature range 300–600 K. Two diffuse phase transitions were observed in Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃. The anomaly near 530 K for y = 0.43 is responsible for the transition from the rhombohedral phase to the tetragonal one. For y > 0.44 this transition is found to be very diffuse and the coexistence of rhombohedral and tetragonal phases occurs. The observation of low piezoelectric activity confirms the existence of polar regions in Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃ above T _m.     

Micro‐Raman study of Zr‐substituted Bi4Ti3O12 ceramics

We have studied the lattice vibrational modes of Zr‐substituted Bi₄Ti₃O₁₂ ceramics using micro‐Raman spectroscopy. Replacement of Zr at the Ti site in the perovskite block is found from the increase in the lattice parameters as a function of Zr contents. Combined X‐ray diffraction patterns and Raman analysis suggested less than 40 mole% Zr solubility in Bi₄Ti₃O₁₂. At 40 mole% of Zr substitution or above, the unreacted monoclinic‐phase ZrO₂ is observed in the X‐ray diffraction patterns and the Raman spectra. The incorporation of Zr in Bi₄Ti₃O₁₂ reduces the soft mode wavenumber and the transition temperature. Moreover, temperature dependent studies confirmed the ferroelectric to paraelectric transition in Bi₄Ti₃O₁₂ at about 675 °C. On increasing the Zr content up to 40% on the Ti sites of Bi₄Ti₃O₁₂, a systematic decrease in the phase transition temperature from 675 to 630 °C was observed. Copyright © 2007 John Wiley & Sons, Ltd.     

Temperature‐dependent Raman scattering studies of the geometrically frustrated pyrochlores Dy2Ti2O7, Gd2Ti2O7 and Er2Ti2O7

The temperature‐dependent Raman studies of A₂Ti₂O₇(A = Dy, Er, Gd) were performed on single crystals and polycrystalline samples in the 4.2–295 K temperature range. The Raman spectra showed softening of the majority of phonon modes upon cooling in the whole temperature range studied and large decrease of linewidths. These changes have been analyzed in terms of strong third‐order phonon–phonon anharmonic interactions. Moreover, the 312 and 330 cm⁻¹ modes of Er₂Ti₂O₇(Gd₂Ti₂O₇) showed hardening upon cooling down to about 130 K (100 K) and then anomalous softening below this temperature. The observed anomalous behavior of the Raman modes indicates that some important changes occur in these materials at low temperatures. However, the origin of this behavior is still not clear. Copyright © 2008 John Wiley & Sons, Ltd.     

Structural and impedance spectroscopy study of Samarium modified Barium Zirconium Titanate ceramic prepared by mechanochemical route

Samarium modified Barium Zirconium Titanate (BZT) ceramics with general formula [Ba_1−xSm_2x/3](Zr_0.05Ti_0.95O₃) [x = 0, 0.01, 0.02, 0.03 and 0.04] have been prepared by high energy ball milling. The Rietveld refinement of BaZr_0.05Ti_0.95O₃ (BZT) shows a single phase tetragonal symmetry with space group P4mmm and TEM micrograph shows that the crystalline size is in the submicron range. X-ray diffraction (XRD) patterns confirm that no phase change occurs with the addition of Samarium in BZT upto x ≤ 0.03 and a small pyrochlore phase exists at x = 0.04. The complex impedance (Nyquist) plots display a single semicircle highlighting the influence of grain resistance on the electrical behavior. Negative temperature coefficient of resistance behavior is observed in all compositions. The activation energy calculated from Z″ and DC conductivity confirms that the oxygen vacancies play an important role in the conduction mechanism.     

Tuning of phonon anharmonicity in pyrochlore titanates: temperature‐dependent Raman studies of Sm2Ti2‐xZrxO7 (x=0, 1/2, 3/4, and 2) and stuffed spin‐ice Ho2 + xTi2 − xO7 − x/2 (x=0, 1/3, and 2/3)

Anomalous temperature dependence of Raman phonon wavenumbers attributed to phonon–phonon anharmonic interactions has been studied in two different families of pyrochlore titanates. We bring out the role of the ionic size of titanium and the inherent vacancies of pyrochlore in these anomalies by studying the effect of replacement of Ti^{4 +} by Zr^{4 +} in Sm₂Ti₂O₇ and by stuffing Ho^{3 +} in place of Ti^{4 +} in Ho₂Ti₂O₇ with appropriate oxygen stoichiometry. Our results show that an increase in the concentration of the larger ion, i.e. Zr^{4 +} or Ho^{3 +}, reduces the phonon anomalies, thus implying a decrease in the phonon–phonon anharmonic interactions. In addition, we find signatures of coupling between a phonon and crystal field transition in Sm₂Ti₂O₇, manifested as an unusual increase in the phonon intensity with increasing temperature. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of Ba-substitution on the structural and ferroelectric properties of Pb1− x Ba x Zr0.40Ti0.60O3 ceramic materials

This work presents a comprehensive study about the influence of Ba-substitution on the structural and ferroelectric properties of Pb_1?x Ba _x Zr_0.40Ti_0.60O₃ (PBZT) ceramic system. Pb_1?x Ba _x Zr_0.40Ti_0.60O₃ ceramic samples were then prepared by solid state reaction method and characterized as a function of composition and temperature by X-ray diffraction (XRD) and impedance spectroscopy techniques. The dielectric measurements show that the substitution of Pb²⁺ for Ba²⁺ ions leads to a diffuse behavior of the dielectric permittivity curves for all samples and that only the x?=?0.50 sample presents a typical relaxor behavior. In good agreement with dielectric measurements, the structural phase transition study showed a phase transition from a tetragonal structure with P4mm space group to a cubic structure with Pm-3m space group for all samples, except for the x?=?0.50 sample were a cubic structure was observed in the complete temperature interval measured.     

Electrical studies on Zr-modified Bi3.25La0.75Ti3O12: a promising FRAM ceramic

Zr-modified Auruvillius family of lanthanum bismuth titanate, namely Bi_3.25La_0.75Ti_3?xZr_xO₁₂ (BLTZ, x = 0, 0.1, 0.3, 0.5, 0.7 and 1), was prepared by solid-state reaction method. Dielectric properties of the ceramics were studied as a function of temperature. Hysteresis measurements were also performed. Among the composition, Bi_3.25La_0.75Ti_2.9Zr_0.1O₁₂ (BLTZ1) showed large remnant polarization compared to the promising ceramic, namely Bi_3.25La_0.75Ti₃O₁₂. The results were corroborated with the pyroelectric, electric polarization and Raman spectroscopic data.     

Abnormal Raman spectra in Er‐doped BaTiO3 ceramics

Greatly enhanced and abnormal Raman spectra were discovered in the nominal (Ba_{1 − x}Er_x)Ti_{1 − x/4}O₃ (x = 0.01) (BET) ceramic for the first time and investigated in relation to the site occupations of Er³⁺ ions. BaTiO₃ doped with Ti‐site Er³⁺ mainly exhibited the common Raman phonon modes of the tetragonal BaTiO₃. Er³⁺ ions substituted for Ba sites are responsible for the abnormal Raman spectra, but the formation of defect complexes will decrease spectral intensity. A large increase in intensity showed a hundredfold selectivity for Ba‐site Er³⁺ ions over Ti‐site Er³⁺ ions. A strong EPR signal at g = 1.974 associated with ionized Ba vacancy defects appeared in BET, and the defect chemistry study indicated that the real formula of BET is expressed by (Ba_{1 − x}Er_3x/4)(Ti_{1 − x/4}Er_x/4)O₃. These abnormal Raman signals were verified to originate from a fluorescent effect corresponding to ⁴S_3/2→⁴I_15/2 transition of Ba‐site Er³⁺ ions. The fluorescent signals were so intense that they overwhelmed the traditional Raman spectra of BaTiO₃. The significance is that the abnormal Raman spectra may act as a probe for the Ba‐site Er³⁺ occupation in BaTiO₃ co‐doped with Er³⁺ and other dopants. A new broad EPR signal at g = 2.23 was discovered, which originated from Er³⁺ Kramers ions. Copyright © 2014 John Wiley & Sons, Ltd.     

Investigation of the ferroelectric–relaxor crossover in Ce-doped BaTiO3 ceramics by impedance spectroscopy and Raman study

BaCe _x Ti_{1? x} O₃ (x?=?0.06, 0.10, and 0.20) solid solutions were prepared via conventional the solid-state reaction and sintered at 1500°C for 4?h, resulting in dense single phase ceramics with homogeneous microstructures. The electric field dependence of permittivity of the BaCe _x Ti_{1? x} O₃ ceramics was investigated in detail, together with the ferroelectric–paraelectric phase transition features. A transformation from normal to relaxor ferroelectrics was observed by increasing the Ce concentration. For low-Ce content, a substitution of Ce on both A and B site positions was proposed from the dielectric study and confirmed by Raman analysis.     

Temperature‐dependent Raman scattering in ferroelectric Bi4−xNdxTi3O12(x = 0, 0.5, 0.85) single crystals

The temperature‐dependent Raman spectra of ferroelectric Bi_4−xNd_xTi₃O₁₂(x = 0, 0.5, 0.85) single crystals were recorded from 100 to 800 K. It was found that there is a critical Nd content x₀ between 0.5 and 0.85. The Nd³⁺ ions prefer to replace Bi³⁺ ions in pseudo‐perovskite layers when x < x₀, while they might begin to incorporate into (Bi₂O₂)²⁺ layers when x ≥ x₀. Nd substitution leads to a decrease in the ferroelectric–paraelectric transition temperature (T_c). A monoclinic distortion of orthorhombic structure occurs in Bi₄Ti₃O₁₂ crystals at temperatures below 200 K. Copyright © 2009 John Wiley & Sons, Ltd.     

High-temperature soft phonon behaviour in PLZT 8/65/35 relaxor ferroelectrics

Polar phonons in infrared spectra of (Pb_0.88La_{0.08 0.04})(Zr_0.65Ti_0.35)O₃ ceramics and thin films exhibit similar behaviour. Each phonon allowed in perfect cubic lattice is split not only below the Burns temperature T _B = 620 K, where it can be explained with breaking of cubic symmetry in polar nanoclusters, but also above T _B. We explain it with two chemical species at both A and B perovskite sites. The E component of the soft mode remains heavily damped at all temperatures and its frequency near 35 cm^?1 is almost temperature-independent. The A₁ component of the soft mode remarkably hardens below T* ≈ 500 K from 50 to 85 cm^?1 and moreover a new mode activates in IR spectra below 300 K at frequencies between A₁ and E soft modes. Based on comparison with other relaxors, we conclude that such behaviour is general for all relaxor ferroelectrics with perovskite structure.