Properties Of Lead Magnesium Niobate Research Articles

AC conductivity and dielectric analysis of Pb1-xLax[(Mg1+x/3Nb2-x/3)0.65Ti0.35(1-x)/4]O3, (x = 0, 0.02, 0.05) relaxor ferroelecric ceramics

In this paper we investigate the effect of lanthanum doping on structural, dielectric and electrical properties of lead magnesium niobate - lead titanate, 0.65Pb(Mg1/3Nb2/3O3)- 0.35PbTiO3 (x=0, 0.02, 0.05) ferroelectric ceramics. Dielectric and AC impedance spectroscopic measurements were carried out on pure and lanthanum doped PMN/PT ceramics over a wide temperature (30o- 450o C) and frequency interval (10 Hz-1 MHz). Pure and lanthanum doped Pb1-xLax[(Mg1+x/3Nb2-x/3)0.65Ti0.35(1-x/4)]O3, (x=0, 0.02, 0.05) ceramics were prepared by solid state reaction route using columbite precursor method. X-ray diffraction revealed tetragonal (P4mm) phase for pure PMN/PT ceramics and transition to pseudo cubic phase (Pm3m) was observed with increased lanthanum doping. The dielectric response of the lanthanum modified PMN/PT ceramics was interpreted in terms of modified curie weiss law. Modulus spectroscopy revealed the deviation of dielectric behavior from ideal Debye behaviour. Activation energies calculated from dielectric relaxation and modulus spectroscopy suggested that charge transport processes are due to oxygen ion hopping.The AC conductivity of the PMN/PT ceramics initially increased for 2 mol% of lanthanum doping followed by a subsequent decrease with further 5 mol% of lanthanum doping. The value of the activation energies calculated from the temperature dependance of ac conductivity was in the range from 1.20-1.48 ev which is due to doubly ionized oxygen vacancies. The overall structural, electrical and dielectric behaviour of Pb1-xLax[(Mg1+x/3Nb2-x/3)0.65Ti0.35(1-x/4)]O3, (x=0, 0.02, 0.05) ceramics is correlated to the relaxor nature induced by lanthanum doping.

Structural and dielectric properties of Lead Magnesium Niobate and Ti-doped Lead Magnesium Niobate at room temperature

Lead based relaxor ferroelectric like Lead Magnesium Niobate and their binary solid solutions with Lead Titanate have great interest of research because of their significant and excellent dielectric, piezoelectric and electrostrictive properties. In the present work, the Lead Magnesium Niobate (PMN) and Lead Magnesium Niobate-Lead Titanate (0.75PMN-0.25PT) were prepared through solid state reaction method with double sintering process at 1200 °C for 6 hr. XRD data shows the pervoskite structure of the prepared sample. SEM report of PMN and 0.75PMN-0.25PT shows the different microstructure with dense grains. Dielectric study of PMN and 0.75PMN-0.25PT shows the effect of addition of PT content on electrical properties at room temperature.

Modification of Relaxor and Impedance Spectroscopy Properties of Lead Magnesium Niobate by Bismuth Ferrite

The relaxor and impedance characteristics of classic or traditional lead magnesium niobate (PbMg1/3Nb2/3O3; PMN) ferroelectric relaxor material have been modified by chemically synthesizing with multiferroic bismuth ferrite (BiFeO3; BFO). Detailed studies of structural, morphological and electrical properties of PMN-BFO-prepared solid solutions [((Pb1−xBix) (Mg0.33(1−x)Nb0.66(1−x)Fex) O3) with x = 0.1, 0.2, 0.3 and 0.4] reveal some interesting findings on structure–properties relationships. The formation of single phase material of each compound in orthorhombic crystal system is identified from x-ray diffraction. The microstructure analyses reveal that the grain size of PMN-BFO increases for increasing BFO weight percent with PMN. The increase of BFO concentration not only improves the dielectric response of PMN-BFO but also modifies the nature of attained phase transition from a typical relaxor to a normal ferroelectric. The impedance spectroscopy studies exhibit the presence of grain and grain boundary effects, and the existence of a positive temperature coefficient of resistance (PTCR) in the material. The ac conductivity increases with the increase in frequency in the low-temperature region for larger content of BFO in the solid solutions. It is observed that the prepared electronic materials obey the non-Debye-type of conductivity relaxation behavior.

Effects of Electrodes on Dielectric and Piezoelectric Properties of Lead Magnesium Niobate–Lead Titanate Single-Crystal Transducer

Effects of Electrodes on Dielectric and Piezoelectric Properties of Lead Magnesium Niobate–Lead Titanate Single-Crystal Transducer

Dielectric Properties of Lead Magnesium Niobate and Lead Iron Niobate Prepared by the Semiwet Hydroxide Route

Lead magnesium niobate (PMN) and lead iron niobate (PFN) were prepared by the semiwet hydroxide route, and their dielectric properties were measured in temperature ranges around their peak dielectric constants. The dielectric constant of PFN was much larger as compared with that of PMN sintered at the same temperature. The dielectric properties of PMN and PFN are compared and explained on the basis of their structure development.

Effect of humidity on dielectric properties of lead magnesium niobate containing excess MgO

The enhancement of dielectric constant (K) in humid atmosphere (K max = 13360 in dry atmosphere to 17450 in 100% relative humidity) for lead magnesium niobate [Pb(Mg 1/3Nb 2/3)O 3] relaxor materials sintered at 950°C for 30 min (using 3 wt% excess Pbo as a sintering aid) can be explained by the extended low frequency dispersion (LFD) model proposed earlier. However, it has been observed that for samples containing excess MgO, such enhancement of K max in humid atmosphere is not so remarkable. It has been shown that in case of samples containing excess MgO, owing to the presence of already formed OH − ions at the surface arising out of the reaction of adsorbed moisture with MgO, the physical absorption of polar H 2O molecules in humid atmosphere will be much less and consequently the enhancement of dielectric response in humid atmosphere should be low.

B-site ordering and dielectric relaxation properties of lead magnesium niobate

The mechanism of order-disorder of Lead Magnesium Niobate on B-site was examined by both the heat treatment and La+3-doping methods. Pyrochlore phase appeared with the increase of La+3-doping concentration was also studied. The effect on dielectric properties, such as the increase of degree of diffuse phase transition in both the annealed and La+3 -doped specimen, was interpreted as a formation of Mg2+/Nb5+=1 non-stoichiometric short-range ordered micro-domains accompanied with segregation of Nb5+ in the disordered area. It was demonstrated that kinetic mechanism of growth of ordered micro-domains was controlled by ion diffusion during both the annealing and La+3-doping.

Relationships between sintering conditions, microstructure and dielectric properties of lead magnesium niobate

Lead magnesium niobate, (Pb(Mg 1/3Nb 2/3)O 3; PMN) ceramics have been produced by sintering PMN powders synthesized from lead oxide (PbO) and magnesium niobate (MgNb 2O 6). As these PMN powders could be prepared in a reproducible manner, attention has been focused on relationships between sintering conditions, phase formation, density, microstructural development and dielectric properties. A method has been developed whereby volatilisation of PbO can be minimised, thereby avoiding the formation of pyrochlore phases and maximising the perovskite yield. The optimum sintering conditions have been identified as 1275 °C for 2 h.

Role of excess PbO on the microstructure and dielectric properties of lead magnesium niobate

Stoichiometric and 2 wt. % excess lead oxide containing lead magnesium niobate (PMN) ceramics have been prepared by partial oxalate route. Dielectric measurements with frequency showed a typical relaxor behavior for stoichiometric PMN, while PMN with excess PbO shows a scatter in the dielectric curves at all temperatures above Tc. Under the same processing conditions, the dielectric constant (Kmax) decreases drastically from 16,300 to 9500 at 1 KHz for PMN without and with excess PbO, respectively. Microstructure studies revealed a second phase (unreacted PbO) segregated in the grain boundaries for excess PbO samples. A careful analysis of the data on dielectric properties and phases present coupled with microstructural detail indicate that the second phase in the grain boundary has a pronounced effect on the dielectric properties and not the pyrochlore phase.

Mechanism of Diffuse Phase Transition in Relaxor Ferroelectrics

Dielectric properties of lead magnesium niobate (PMN) and Ta-bearing strontium barium niobate (SBNT) were measured as a function of temperature, and the crystal structure of PMN was refined by the Rietveld analysis method. The results of structure refinement indicate that the volume of polar microregions (PMR) increases with decreasing temperature. The dielectric properties of PMN and SBNT are well explained by an advanced theory of dielectric dispersion. The anomalous behavior in dielectric permittivity (ε) observed on the low temperature side of T m, the temperature of ε maximum, is explained by simple dielectric relaxation, while on the high-temperature side of T m is explained by the volume increase of PMR. It is concluded that these is no phase transition around T m, and the diffuse phase transition is an overlapping phenomenon of volume increase of PMR, freezing process of fluctuating dipoles in PMR and dielectric dispersion around the measuring frequrncy. A model of diffuse phase transition and relaxor ferroelectrics is proposed. The difference between normal ferroelectrics and relaxor ferroelectrics is discussed from the viewpoints of spreading of soft-mode phonons and disorder in the crystals.

Influence of heterovalent doping on the degradation properties of lead magnesium niobate

The perovskite material ABO3 with A = Pb and B = (Mg, Nb, Ti) has been doped with donors and acceptors in sites A and B. Because of the peculiar properties of this material (ordered nanodomains within a disordered phase), the effects of the dopants are different from those observed for classical perovskites like BaTiO3. Mn and W improve the degradation properties during the accelerated life test. This is interpreted by the built-in internal field observed after the degradation test on the ferroelectric hysteresis loops. This internal field is due to dipolar associated defects also responsible for ageing. Perovskitmaterialien der Zusammensetzung ABO3, A = Pb und B = (Mg, Nb, Ti) wurden mit Donoren und Akzeptoren auf Gitterplätzen vom Typ A und B dotiert. Aufgrund der speziellen Struktureigen-schaften dieser Materialien (geordnete Nanodomäne eingebettet in eine ungeordnete Matrix), zeigt die Dotierung andere Effekte als in klassischen Perovskitmaterialien wie BaTiO3. Die Autoren finden eine Verbesserung der Alterungseigenschaften unter Dotierung mit Mn und W. Dies wird durch den Eingluß eines inneren Feldes zurückgeführt, das durch assoziierte Defekte mit Dipolmoment erzeugt wird. Der Nachweis des inneren Feldes erfolgt in Hysteresemessungen, die nach dem Alterungstest durchgeführt wurden. Le matériau pérovskite ABO3 avec A = Pb et B = (Mg, Nb, Ti) a été dopé avec des donneurs et des accepteurs en site A et B. En raison des propriétés particulières de ce matériau (présence de nanodomaines ordonnés dans une matrice désordonnée), l'effet des dopants est différent de celui observé sur les pérovskites plus classiques comme BaTiO3. Mn et W améliorent l'endurance durant le test de dégradation accélérée. Cela est interprété par la présence d'un champ interne observé sur les cycles d'hystérésis après le test de dégradation. Ce champ interne est dû à des défauts associés ayant un moment dipolaire et également responsables du vieillissement en l'absence de champ extérieur.

The Role of Excess Magnesium Oxide or Lead Oxide in Determining the Microstructure and Properties of Lead Magnesium Niobate

Near‐phase pure perovskite lead magnesium niobate (PMN) with MgO or PbO additives was produced by reacting PbO with MgNb2O6 at 800°C and sintering at 1200°C. Dense ceramics were characterized by scanning electron microscopy, X‐ray diffraction, and dielectric measurements. The microstructural studies showed that excess MgO exists as micrometer spherical particles either in the grain boundary as a discrete particle or in the perovskite grain as an inclusion. The pyrochlore phase exists in large isolated grains in the microstructure. The 10 mol% MgO excess composition had a peak dielectric constant of 19 500 at 100 Hz, which suggests very “clean” or uninhibiting grain boundaries. The excess addition of PbO did not improve the yield of perovskite PMN phase and decreased the dielectric constant. PMN grain boundaries are the dominant path of fracture. This paper, to a certain degree, explores the chemistry and characteristics of these grain boundaries.

Microstructure and Dielectric Properties of Lead Magnesium Niobate‐Pyrochlore Diphasic Mixtures

The microstructure and dielectric properties of lead magnesium niobate (PMN) ceramics containing the determental second phase, pyrochlore, have been studied. The pyrochlore phase within PMN was found to be present as isolated grains in the microstructure with a composition of Pb2(Mg0.25Nb1.75)O6.625 and a preferred octahedral morphology. The amount of pyrochlore second phase can be easily controlled by changing the Mg/Nb ratio on the B‐site of the perovskite structure, and a series of diphasic mixtures from near‐pure PMN to near‐pure pyrochlore were obtained. Its effect on the permittivity follows the isolated Wiener's mixture rule up to a pyrochlore content of 18 vol%.

Dielectric properties due to excess PbO and MgO in lead magnesium niobate ceramics

Abstract The dielectric properties of lead magnesium niobate (PMN) have been investigated as a function of the amount of excess PbO and excess MgO in the range of 0–40 m/o and 0–150 m/o, respectively. In the case of PMN with both 40 m/o excess PbO and 5 m/o excess MgO added, the pyrochlore phase was completely eliminated. And there was great increase in grain size and dielectric constant as compared to PMN with no excess MgO. But in the range of 10–150 m/o excess MgO, the dielectric constant tended to decrease with increase in the amount of excess MgO even though no pyrochlore phase was found to be present. Also, the MgO rich second phase appeared to precipitate. These results can be explained by microstructure analysis.

A macroscopic theory for the dielectric properties of lead magnesium niobate

Lead magnesium niobate (Pb3MgNb2O9) is a cubic perovskite-type crystal which shows strong relaxation behaviour in the dielectric properties. Based on recent electron diffraction studies which show ordering of the Mg and Nb ions in this structure, and suggest a lamellar superlattice 'domain' structure, a particularly simple model is proposed to account for the electrical behavior. Based on this model a comparison is made with dielectric, structural, and electro-optic properties.