Structural and electrical studies in La-substituted SrBi2Nb2O9 ferroelectric ceramics (original) (raw)
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Dielectric studies of La and Pb doped SrBi2Nb2O9 ferroelectric ceramic
Materials Letters, 2006
In this paper, structural and dielectric studies of Sr 1−x A x Bi 2 Nb 2 O 9 (A = La, Pb and x = 0.2) ceramics are reported. Tetragonal strain decreases on introduction of lanthanum while it increases for the lead doped sample. Addition of lead increases Curie temperature and sample with lanthanum content shows remarkable decrease in Curie temperature with broadened dielectric peak. The sample with x = 0.0 shows a rapid fall in dielectric constant value above 100 KHz. The lanthanum and lead doped samples show reduced dielectric loss values with frequency.
Ferroelectric Properties of the La 0.03 Sr 0.225 Ba 0.7 Nb 2–y Ti y O 6–y/2 Ceramic System
Journal of Electroceramics, 1999
The study of the dielectric properties of the stoichiometric Titanium doped Sr0.255La0.03Ba0.7Nb2O6 ceramics prepared according to the formula Sr0.225La0.03Ba0.7Nb2–yTiyO6–y/2 is reported. A single phase compound is observed for low Ti content (yy<0.1), the XRD patterns show, besides the SBN phase reflections, several small peaks associated with an additional phase present in the ceramics. A possible liquid phase sintering is analyzed.
Lead-free 0.96[Bi 1/2 (Na 0.84 K 0.16 ) 1/2 ] (1Àx) La x TiO 3 -0.04SrTiO 3 (BNKTLax-ST, with x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) ceramics have been synthesized using a conventional solid-state reaction method and their phase transition, dielectric, ferroelectric, and strain properties investigated. X-ray diffraction patterns revealed formation of pure perovskite phase. A phase transition from coexistence of rhombohedral and tetragonal to a pseudocubic phase was observed at x = 0.02. Polarization and bipolar strain hysteresis loops indicated that the ferroelectric order (FE) of BNKT-ST is significantly disrupted by lanthanum doping. The destabilization of the FE order results in degradation of the remanent polarization, coercive field, depolarization temperature (T d ), electromechanical coupling factor (k p ), and static d 33 , accompanied by large electric-field-induced strain of 0.34% at 60 kV/cm with normalized strain of d 33 * = S max /E max = 600 pm/V at a critical composition of around x = 0.02.
In this work, (Na 0.5 Bi 0.5) 0.94 Ba 0.06 TiO 3 ceramic doped with three lanthanides La 3+ , Gd 3+ , Ho 3+ were prepared and investigated the corresponding structural, vibrational, ferroelectric and energy storage properties. The X-ray diffraction and Raman spectra reveal a pure perovskite with the coexistence of rhombohedral and tetragonal phases at room temperature for all samples. The thermal dependence of the dielectric constant shows a ferroelectric/antiferroelectric phase transition around T d , confirmed by the change in the shape of P-E hysteresis loops for all samples. We found that the optimal piezoelectric and ferroelectric properties were obtained in the ceramic doped with Ho 3+. Furthermore, the later sample revealed relatively remarkable features of energy storage density with temperature, reaching a maximum of 0.63 J/cm 3 around 100 • C. The results discussed in this work highlight the great potential of the doped NBT-6BT based lead-free ceramics.
Phase transition and electrical studies of wolframium doped SrBi 2 Ta 2 O 9 ferroelectric ceramics
Journal of Electroceramics, 2006
In this study, crystalline structure, dielectric and impedance properties of SrBi2Ta2O9 (SBT) - based ferroelectric ceramics have been investigated with the substitution of wolframium/tungsten (W) onto the tantalum site. Wolframium doped SrBi2(Wx Ta1 − x )2O9 (0.0 ≤ x ≤ 0.20) ceramics were synthesized by solid state reaction method. The X-ray diffractogram analysis revealed that the substitution formed a single phase layered perovskite structure for the doping content up to x ≤ 0.05. The dielectric measurements as a function of temperature show an increase in Curie temperature (T c ) over the composition range of x = 0.05 to 0.20. The W6 + substitution in perovskite-like units results in a sharp dielectric anomaly at the ferroelectric phase transition. Furthermore, the dielectric constant at their respective Curie temperature increases with wolframium doping. Both enhanced Curie temperatures and dielectric constants at the Curie points indicate an increase in polarizability, which could be attributed to the increased “rattling space” due to the incorporation of the smaller tungsten cations. The dielectric loss reduces significantly with tungsten addition. AC impedance properties vis-à-vis wolframium content has also been studied.
Structural and dielectric properties of SrxBa1− xNb2O6 ferroelectric ceramics
This paper reports, the structural, dielectric and transport properties of Sr x Ba 1− x Nb 2 O 6 [SBN] for x =0.4 and 0.5, prepared by traditional sintering method (solid state reaction technique). The tetragonal tungsten bronze type crystal structure, structural parameters such as the lattice constant (a =12.63946Å, b = 12.63946Å, c =3.978203462Å), average crystallite size (61.62 nm-95.17nm ), and texture coefficient (TC) have been determined using X-ray diffraction data. TGA-DTA analysis reveals that formation of oxide phase takes place beyond 1050 • C. Rod shaped surface morphology has been obtained. The fundamental vibrational mode observed in finger print region by FTIR reveals formation of SBN ceramics. The variation of real of part dielectric constant (έ) and loss tangent (tanδ) was studied at room temperature. The dispersion of dielectric constant with frequency indicates relaxor nature of SBN.
Dielectric properties and microstructure of Sr 0.8(K,Na) 0.2Bi 2Nb 2O 9 ferroelectric ceramics
Journal of Alloys and Compounds, 2009
The influence of the microstructure on dielectric properties of Sr0.8(K,Na)0.2Bi2Nb2O9 (SKNBNO) prepared by the solid-state route is reported. The formation of Bi-layer structure was obviously restrained owing to the K and Na ions substituting Sr ions by the X-ray diffraction analysis (XRD) and scanning electron micrograph (SEM). At the same time, some slight secondary phase of bismuth oxide was detected but the structure was not changed. The dielectric constant was restrained by K and Na ions substituting Sr ions, which is mainly attributed to the slight change of lattice constants resulting in a decreased “rattling space” for the cations inside the distorted Nb(V)O6 oxygen octahedron of the perovskite block. A clear enhancement in the stability of frequency and temperature was noticed for SKNBNO sample compared to Sr2Bi2Nb2O9 (SBN) samples.
Comparison of strain and ferroelectric properties of La,Nb and Li,Nb co-modified BNKT-ST ceramics
Research Square, 2020
A comparison between the influence of concurrent A and B-site acceptor-donor (Li,Nb) and donor (La,Nb) doping in Pb-free Bi 0.5 (Na 0.84 K 0.16 ) 0.5 TiO 3 –SrTiO 3 piezoelectrics on structure, ferroelectric and the high voltage induced strain were made. In this work, Lithium was chosen as acceptor and Lanthanum was chosen as donor dopant on A-site and Nb 5+ as a B-site donor. Both modifier impurities promoted a phase evolution from the coexistent of two-phase structures (rhombohedral tetragonal) into a more symmetric single pseudocubic structure. Nonetheless, (La,Nb) donor-donor doping induced the phase transition at 1 mol%, while (Li,Nb) acceptor-donor doping at 2 mol%. Interestingly, acceptor-donor (Li,Nb) co-substitution results in the broadening of ergodic relaxor and ferroelectric (ER-FE) mixed phase boundary which is favourable for multidevice applications. This comparative study show that the A-site vacancies play a substantial role to induce the phase transformation from nonergodic-ergodic relaxor (NR-ER) and the improvement in their high voltage induced strain.
Journal of Alloys and Compounds, 2011
LiSbO 3 doped Sr 0.53 Ba 0.47 Nb 2 O 6 ceramics were synthesized by conventional mixed-oxide method. The phase structure, microstructure, dielectric and ferroelectric properties of obtained ceramics were investigated. Pure tungsten bronze structure could be obtained in all ceramics and LiSbO 3 additive could promote densification and reduce the sintering temperature. The dielectric characteristics showed diffuse phase transition phenomena for all samples, which was proved by linear fitting of the modified Curie-Weiss law with value varying between 1.65 and 1.92. With increasing LiSbO 3 content, the transition temperature T c decreased gradually to near room temperature. Normal ferroelectric hysteresis loops could be observed in all compositions, but the remnant polarization (P r) and coercive field (E c) all decreased gradually. Besides, the underlying mechanism for variations of the electrical properties caused by LiSbO 3 doping was explained in this work.