Mn-doped Ceramics Research Articles

Multiferroic property, dielectric response and optical behavior of filled tungsten bronze Ba4Nd2Fe2-xMnxNb8O30 (0 ≤ x ≤ 1) ceramics

In this paper, the structural, magnetic, dielectric, ferroelectric and optical properties of Mn doped tungsten bronze Ba4Nd2Fe2-xMnxNb8O30 (0 ≤ x ≤ 1) ceramics were investigated in detail. All the samples are of single phase with the tetragonal structure and the group space of P4bm. Compared with antiferromagnetism in pure sample, Mn-doped samples show a weak room-temperature ferromagnetic state. The observed ferromagnetism in Mn-doped ceramics can be understood in terms of the AFM coupling of Fe-based and Mn-based sublattices via Dzyaloshinskii-Moriya interaction. The relaxor ferroelectric nature can be demonstrated in the doped samples. The sample x = 0.5 exhibits a high storage energy density U of 1.06 J/cm3 and efficiency η of 94.3%. The low-temperature dielectric relaxation obeys well with Vogel-Fulcher relation and can be ascribed to the local polarization fluctuation, while the dielectric relaxation around 300 K follows with Arrhenius law and can be attributed to the localized hopping process of electrons. In addition, the optical band gap decreases from 2.64 eV to 2.49 eV with increasing the Mn concentration.

Defect engineering of BCZT-based piezoelectric ceramics with high piezoelectric properties

The intrinsic conduction mechanism and optimal sintering atmosphere of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) ceramics were regulated by Mn-doping element in this work. By Hall and impedance analysis, the undoped BCZT ceramics exhibit a typical n-type conduction mechanism, and the electron concentration decreases with the increasing oxygen partial pressure. Therefore, the undoped ceramics exhibit best electrical properties (piezoelectrical constant d33 = 585 pC·N−1, electro-mechanical coupling factor kp = 56%) in O2. A handful of Mn-doping element would transfer the conduction mechanism from n-type into p-type. And the hole concentration reduces with the decreasing oxygen partial pressure for Mn-doped BCZT ceramics. Therefore, the Mn-doped ceramics sintered in N2 have the highest insulation resistance and best piezoelectric properties (d33 = 505 pC·N−1, kp = 50%). The experimental results demonstrate that the Mn-doping element can effectively adjust the intrinsic conduction mechanism and then predict the optimal atmosphere.

Peculiarities of specular infrared reflection spectra of ZnO-based ceramics

Undoped and Mn-doped ZnO ceramics were theoretically and experimentally investigated using specular infrared reflection method. It was shown that infrared reflection spectra can be modeled using the parameters explored for ZnO single crystals. For ceramic samples, it was shown that ZnO grains with orientation of the C-axis along the normal to the electric field ( ) give the main contribution to IR reflection spectra. It has been ascertained that the surface roughness is manifested in these spectra mainly within the range 450…550 cm–1 giving negligible effect for the frequencies above longitudinal phonon frequency. This allowed the electrophysical parameters of ZnO crystallites to be evaluated. In the case of undoped ceramics, the obtained results were found to be consistent with the values of direct current measurements. This finding supports the utility of infrared spectroscopy for determination of the electrophysical parameters of polycrystalline ceramic materials. For Mn-doped ceramic samples, the conductivity value measured using the direct current method was found to be essentially lower than those determined from simulation of infrared reflection spectra. This phenomenon was explained by barrier formation at the grain boundaries in Mn-doped ZnO ceramics.

Dielectric Relaxation, Local Structure and Lattice Dynamics in Mn-Doped Potassium Tantalate Ceramics.

Alkaline niobate and tantalate perovskites have attracted attention as polar dielectrics for electronics and telecommunications. Here, we studied the polar behaviour, lattice dynamics, and local structure in conventionally processed K0.985Mn0.015TaO3±δ ceramics using a combination of variable-temperature dielectric and Raman spectroscopies, and X-ray absorption fine structure (XAFS) measurements, respectively. Mn doping induces a low-frequency dielectric relaxation in KTaO3 (KT), which follows the Arrhenius law with an activation energy U ≈ 105 meV and the characteristic relaxation time τ0 ≈ 4.6 × 10−14 s. Our XAFS results support preferential Mn occupancy of the cuboctahedral sites as Mn2+, with these cations strongly off-centred in the oversized oxygen cages. Such disordered Mn displacements generate electric dipoles, which are proposed as the source of the observed dielectric relaxation. We show that in Mn-doped ceramics, the low-frequency polar TO1 mode softens on cooling and, at low temperatures, exhibits a higher frequency than in undoped KT. This mode displays no detectable splitting, which contrasts with Li-doped KT that also contains off-centred Li+ species on the cuboctahedral sites. Therefore, we conclude that the coupling between the Mn displacements and the lattice is weaker than in the Li case, and Mn-doped KT therefore exhibits a dielectric relaxation but no ferroelectric transition.

Electrical properties, EPR analyses and defect chemistry of Mn-doped 0.675PMN-0.325PT piezoceramics

The morphotropic phase boundary solid solution of 0.675Pb(Mg1/3Nb2/3)O3-0.325PbTiO3 (0.675PMN-0.325PT) were studied. Manganese (Mn) was used as a dopant element in 0.4 mol% and 0.7 mol% ratios because of its multiple oxidation states. Sintering was done either in the air or under an oxygen-rich atmosphere. Both the effect of doping and sintering atmosphere on the electrical properties were reported. The ceramic with 0.4 mol% were exhibited higher properties such as piezoelectric charge coefficient (d33), dielectric constant, polarization values compared to undoped and 0.7 mol% Mn-doped ceramics. Electron paramagnetic resonance (EPR) spectroscopy was used to resolve the oxidation state of Mn in the 0.675PMN-0.325PT structure. The electrical properties were discussed and explained using defect chemistry.

Textured Mn-doped PIN-PMN-PT Ceramics: Harnessing Intrinsic Piezoelectricity for High-power Transducer Applications

Mn-doped PIN-PMN-PT ceramics were 90% [001]C textured by reactive templated grain growth (RTGG) with 5 vol% BaTiO3 microplatelets. Hardened properties such as high coercive field (EC) of 14 kV/cm, low dielectric loss (tan δ) of 0.37-0.66%, and high QM of 496 were obtained. Textured Mn-doped ceramics have TC of 219 °C, and a two times greater low-field d33* of 846 pm/V than random ceramics. Rayleigh analysis of textured PIN-PMN-PT ceramics shows that Mn-doping reduces the relative extrinsic contribution of the piezoelectric response to the strain behavior from 38% to 18% (at 4 kV/cm) by reducing irreversible domain wall motion. Mn-doping also reduced the overall strain response of PIN-PMN-PT, but crystallographic texturing increased the intrinsic piezoelectric response of the lattice as evidenced by the increase in d33 (Berlincourt) from 283 pC/N in random ceramics to 341 pC/N in textured ceramics. These results demonstrate that textured Mn-doped PIN-PMN-PT ceramics are excellent candidates for high-power transducer applications.

Enhanced thermal reliability of Mn-doped (K, Na)NbO3-based piezoelectric ceramics

Improving temperature stability of (K, Na)NbO3-based ceramics can facilitate their development in practical application. In this work, 0.5 mol% Mn elements doped 0.95(Na0.5K0.5)NbO3–0.05(Bi0.5Na0.5)HfO3 (abbreviated as KNN) piezoelectric ceramics are reported. Permittivity–temperature curves reveal that the Mn-doped ceramics have higher Curie temperature and more dispersive orthorhombic–tetragonal phase transition compared with undoped ceramics, which improves the temperature stability of the KNN-based ceramics. The electric-field-induced strain varies less than 22% over a wide temperature range from 20 to 200 °C for the Mn-doped KNN-based ceramics, which is much better than the undoped KNN-based ceramics (variation: 38%). Therefore, our work provided a new promising candidate for temperature-insensitive piezoelectric ceramic devices.

Annealing effects on the structure and properties of Mn-doped (K0.48Na0.52)NbO3 lead-free piezoceramics

The Mn-doped (K0.48Na0.52)NbO3 (KNN) ceramics were annealed in air at 600–800 °C for 16 h and the effects of annealing on the structure as well as the ferroelectric and piezoelectric properties were investigated. The 3 mol% Mn-doped ceramics sintered at 1030–1080 °C were found to be melted after being annealed at 800 °C, and the melting temperature decreased with the increase of Mn content. The TC and TO–T of the ceramics with x ≤ 0.04 shifted significantly to higher temperature after annealing. The annealed ceramics doped with 1–4 mol% Mn possessed a large internal bias field (Ei) of 5.08–6.6 kV/cm, and larger d33 and Qm. The d33 of the 1 mol% Mn-doped ceramics increased from 109 to 124 pC/N after annealed at 600 °C, and the largest Qm, 145, was obtained when the 2 mol% Mn-doped ceramics were annealed at 700 °C.

Enhanced microstructure and electrical properties of Mn-modified Bi0.5(Na0.65K0.35)0.5TiO3 ferroelectric ceramics

Bi0.5(Na0.65K0.35)0.5TiO3 (BNKT) and Mn-modified Bi0.5(Na0.65K0.35)0.5(MnxTi1−x)O3 (BNKMT-103x), (x=0.0–0.5%) ferroelectric ceramics were synthesized by solid-state reaction method. Optimization of calcination temperature in Mn-doped ceramics was carried out for the removal of secondary phases observed in XRD analysis. BNKMT ceramics sintered at 1090°C showed enhanced dielectric, piezoelectric and ferroelectric properties in comparison to pure BNKT. The average grain size was found to increase from 0.35μm in BNKT to 0.52μm in Bi0.5(Na0.65K0.35)0.5(Mn0.0025Ti0.9975)O3 (BNKMT-2.5) ceramics. The dielectric permittivity maximum temperature (Tm) was increased to a maximum of 345°C with Mn-modification. AC conductivity analysis was performed as a function of temperature and frequency to investigate the conduction behavior and determine activation energies. Significant high value of piezoelectric charge coefficient (d33=176pC/N) was achieved in BNKMT 2.5 ceramics. Improved temperature stability of ferroelectric behavior was observed in the temperature dependent P–E hysteresis loops as a result of Mn-incorporation. The fatigue free nature along with enhanced dielectric and ferroelectric properties make BNKMT-2.5 ceramic a promising candidate for replacing lead based ceramics in device applications.

Enhanced Ferroelectric Property of Manganese Doped Lead-free (K0.5Na0.5)NbO3 Ceramics

Lead free bulk ceramics manganese doped ceramics (1-x)(K0.5Na0.5)NbO3-xMnO2 (0 ≤ x ≤0.8 mol%, KNN-Mn-x) were prepared by a conventional solid-state sintering technique. Effects of manganese on the phase structure, morphologies and electrical properties of KNN ceramics were investigated. Mn-doped ceramics exhibited good crystallization and improved ferroelectric property. The XRD results showed the single phase perovskite structure was obtained in Mn-doped KNN ceramics. For KNN-Mn-x ceramics with x = 0.4 mol.%, excellent ferroelectric property was obtained: high remanent polarization Pr = 28.3 μC/cm2 and low coercive field Ec = 13.7 kV/cm, which should be attributed to the single phase perovskite structure and the existence of a morphotropic phase boundary (MPB).

Dielectric and electromechanical properties of Mn-doped 0.2875 Pb(Mg1/3Nb2/3)O3–0.2875 Pb(Yb1/2Nb1/2)O3–0.425 PbTiO3 ceramics

In this study, 0.2875 Pb(Mg1/3Nb2/3)O3–0.2875 Pb(Yb1/2Nb1/2)O3–0.425 PbTiO3 (0.2875PMN–0.2875PYbN–0.425PT) ternary ceramic composition was doped with 1 mol% MnCO3 in order to induce hard character for potential high-power applications. Dense 0.2875PMN–0.2875PYbN–0.425PT ceramics with 1 mol% MnCO3 addition were fabricated after sintering at 1100 °C. e r = 1728, tanδ = 0.35 %, d 33 = 320 pC/N, d 31 = −103 pC/N, Q m = 467, k p = 0.40, k 31 = 0.24, k 33 = 0.49, and T c = 280 °C were measured for Mn-doped ceramics. However, undoped ceramics had e r = 2380, tanδ = 1.95 %, d 33 = 433 pC/N, d 31 = −145 pC/N, Q m = 60, k p = 0.43, k 31 = 0.27, k 33 = 0.48, and T c = 285 °C. Acceptor Mn2+/Mn3+ ions presumably substituted B-site ions in the perovskite structure and formed defect dipole pairs. The electrically “hard” character was induced as a result of the domain wall pinning due to the existing defect pairs. Particularly, increasing Q m from 60 to 467 and decreasing tanδ from 1.95 to 0.35 % after Mn doping showed that Mn-doped 0.2875PMN–0.2875PYbN–0.425PT ceramics with “hard” character are potential candidates for high-power projector and transducer applications.

Sintering Behavior of ZnO: Mn Ceramics Fabricated from Sol-Gel Derived Nanocrystalline powders

Abstract Undoped and Mn doped ZnO ceramics, sintered at 1200 °C, were produced from sol-gel derived nanocrystalline powders calcined at 750 °C. Mn doped powders showed trace amounts of spinel (ZnMn2O4) phase in addition to a dominant zincite phase, while Mn doped ceramics were comprised solely of zincite structure. X-ray mapping of the powders did not reveal any Mn concentrated areas, indicating that the ZnMn2O4 phase was homogeneously distributed with a very small grain size. The grain size of the undoped powders was around 50 nm, and there was a minor increase in the grain size when powders were doped with Mn. Undoped ceramics exhibited grain sizes distributed in the range 2 – 10 μm while Mn doped ceramics displayed slightly smaller grains. Relative densities of the undoped and Mn doped ceramics were measured as 0.695 and 0.950, respectively.

Dielectric properties of 3d transition metal substituted BaTiO3 ceramics containing the hexagonal phase formation

The role of transition metals of the 3d series from V (Z = 23) to Zn (Z = 30) is investigated in modifying the crystallographic phase contents, microstructure and the dielectric properties of BaTiO3 ceramics containing ≤10 at% substituents. All the transition metals brought about the phase conversion to hexagonal BaTiO3 and the hexagonality is found to depend on Ba/Ti ratio as well as the processing conditions including the sintering temperature and the post sinter annealing. The er-T characteristics are modified with increasing hexagonality by way of the tremendous decrease in dielectric constant with broad and diminished emax for the mixed phase ceramics giving way to flat er-T curves for totally hexagonal specimens. Doping with >1% Zn2+ or ≥5% Mg2+ also render the ceramics completely hexagonal indicating that the crystal field effects of the 3d orbital electrons are not the cause for the conversion to hexagonal phase. Electron paramagnetic resonance (EPR) spectra of Mn-doped ceramics reveal the prevalence of defect complexes involving oxygen vacancies and different valence states of Mn occupying the Ti-sites within the corner-sharing as well as face-sharing octahedra present in hexagonal BaTiO3. EPR results also indicate defect complexes involving electron localization at Ti-sites and oxygen vacancies around the face-sharing octahedra. On annealing the ceramics in lower oxygen partial pressures at elevated temperatures leads to the reversion to corner shared (Ti3+–VO) defect complex accompanied by the conversion to cubic/tetragonal phase. The alterations in the oxygen vacancy-metal impurity defect complexes and the modifications in the oxygen close packing are the cause for the prevalence of hexagonal BaTiO3 at room temperature.

Manganese-doping of lead magnesium niobium titanate: Chemical control of dielectric properties

An investigation has been carried out into the acceptor-doping of lead magnesium niobate titanate (PMNT), 0.95{ Pb(Mg 1 3 Nb 2 3 )O 3-0.05PbTiO 3 }, through the introduction of manganese ions. These are added by co-reaction of PMNT powder with MnCO 3 and PbO in a single-stage reaction to sintered ceramics. The technique is found to enhance the sinterability of PMNT in less oxidising CO 2 atmospheres. Furthermore, the dielectric response of the Mn-doped ceramics depends strongly on the sintering atmosphere employed. In air, a rapid transition from relaxor to normal ferroelectric properties takes place upon addition of manganese. However, in CO 2, relaxor properties persist up to concentrations of approximately 8mol% manganese. This difference in behaviour is attributed to varying oxidation states of the manganese ions, it being proposed that that air-sintered samples contain predominantly Mn 3+-ions. In CO 2-sintered samples, by comparison, the manganese ions exist in both + 2 and + 3 oxidation states. The relevance to the formation of dipoles, and to an understanding of relaxor ferro-electric ceramics is brought out, employing arguments based on crystal chemistry. Attention is also given to unresolved questions and to areas of future work.

Donor-Acceptor Charge Complex Formation in Barium Titanate Ceramics: Role of Firing Atmosphere

BaTiO3 ceramics containing Mn acceptors and various Mo, W and Nb donor dopants have been fired in reducing atmosphere and re-oxidized in N2/O2. In single Mn-doped ceramics, Mn2+ is completely oxidized to Mn3+; in N2 containing 50 ppm O2 at T > 800°C. Changes of the Curie point and sample length under reduction and re-oxidation have been detected using dielectric and thermomechanical measurements. Charge compensation and complex formation between acceptors and donors have been observed. In donor-acceptor charge complexes, Mn2+ cannot be oxidized.

Electromechanical Properties of Piezoelectric Ceramics in the PLZT-PZN System

Piezoelectric ceramics with the chemical formula Pb1-xLax[(Zr1-yTiy)1-z(Zn1/3Nb2/3)z]1-x/4O3 (x=0.01–0.06, y=0.3–0.6, z=0.1), which are solid solutions composed of PLZT and PZN (Pb(Zn1/3Nb2/3)O3), have been prepared by hot-pressing at 1150°C, and the dielectric and electromechanical properties have been measured. In these materials the rhombohedral-tetragonal morphotropic phase boundary is located in the range of y=0.40–0.43, where the electromechanical coupling factor k33 exceeds 70%. The keff coupling factor for the thickness mode of a plank-shaped bar also reaches nearly as high as 70% in this range. There exists a proportionality between the dielectric and the mechanical losses in the Mn-doped ceramics.