Dielectric, structural and Raman studies on (Na(0.5)Bi(0.5)TiO(3))((1 - x))(BiCrO(3))(x) ceramic

On the Lanthanide Effect on Functional Properties of 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 Ceramic

The beneficial effects of lanthanide incorporation into 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (BNT-BT) matrix on its functional properties were investigated. The conventional solid-state method was used for synthesizing samples. The structural refinement revealed that all samples crystallized in R3c rhombohedral symmetry. Raman spectroscopy study was carried out using green laser excitation and revealed that no clear perceptible variation in frequency is observed. Dielectric measurements unveiled that the introduction of rare earth obstructed the depolarization temperature promoted in BNT-BT, the diffusive phase transition decreasing with increasing lanthanide size. Only dysprosium addition showed comparable diffusion constant and dielectric behavior as the unmodified composition. Further, the comparison of the obtained ferroelectric hysteresis and strain-electric field loops revealed that only Dy-phase exhibited interesting properties comparing parent composition. In addition, the incorporation of lanthanides Ln3+ into the BNT-BT matrix led to the development of luminescence characteristics in the visible and near infrared regions, depending on the excitation wavelengths. The simultaneous occurrence of photoluminescence and ferroelectric/piezoelectric properties opens up possibilities for BNT-BT-Ln to exhibit multifunctionality in a wide range of applications.

Annealing-Dependent Morphotropic Phase Boundary in the BiMg0.5Ti0.5O3-BiZn0.5Ti0.5O3 Perovskite System

The annealing behavior of (1-x)BiMg0.5Ti0.5O3−xBiZn0.5Ti0.5O3 [(1-x)BMT−xBZT] perovskite solid solutions synthesized under high pressure was studied in situ via X-ray diffraction and piezoresponse force microscopy. The as prepared ceramics show a morphotropic phase boundary (MPB) between the non-polar orthorhombic and ferroelectric tetragonal states at 75 mol. % BZT. It is shown that annealing above 573 K results in irreversible changes in the phase diagram. Namely, for compositions with 0.2 < x < 0.6, the initial orthorhombic phase transforms into a ferroelectric rhombohedral phase. The new MPB between the rhombohedral and tetragonal phases lies at a lower BZT content of 60 mol. %. The phase diagram of the BMT−BZT annealed ceramics is formally analogous to that of the commercial piezoelectric material lead zirconate titanate. This makes the BMT−BZT system promising for the development of environmentally friendly piezoelectric ceramics.

Structure and dielectric properties of (1-x)Bi0.5Na0.5TiO3-xBaTiO3 piezoceramics prepared using hydrothermally synthesized powders

The influence of different processing parameters and various Ba2+ addition (up to 10 mol%) on the structure and dielectric properties of Bi0.5Na0.5TiO3-BaTiO3 (BNT-BT) ceramics was investigated. The powders were hydrothermally synthesized in the alkaline environment at 180°C for different time periods. X-ray diffraction confirmed the presence of dominant rhombohedral Bi0.5Na0.5TiO3 phase and a small amount of secondary pyrochlore Bi2Ti2O7 phase in the pure BNT powders. In addition, one-dimensional Na2Ti2O7 structure was also observed in the powder hydrothermally treated for a long time (i.e. 48 h). The amount of secondary pyrochlore phase in the BNT-BT powders increases with the increase of Ba2+ content. The synthesized powders were pressed into pellets and finally sintered at various temperatures up to 1150°C. High density (more than 90%TD) was obtained in all BNT-BT sintered samples. Optimal sintering parameters were chosen in order to obtain dense ceramics with the optimal phase composition. The temperature dependence of dielectric properties for the BNT-BT ceramics was also studied. Relaxor behaviour of BNT-based ceramics and broad transition peaks are evident in all samples. Dielectric constant up to 400 as well as an acceptable low dielectric loss at temperatures lower than 200°C were obtained in BNT-BT ceramics.

The effects of Fe-doping on MnO2: phase transitions, defect structures and its influence on electrical properties

The composition of Mn_1−xFe_xO₂ (x = 0–0.15) was synthesized by a hydrothermal method at 140 °C for 5 hours of reaction time. Investigations were carried out including XRD, FTIR, Raman spectroscopy, FESEM, and TEM for crystallographic phase analysis. Furthermore, XPS and XAS were used to analyze the oxidation states of Mn and dopant Fe in the octahedron sites. For electrical characterizations, an impedance analyzer was used to explore the conductivity and dielectric properties. It was discovered that the undoped MnO₂ possessed an α-MnO₂ structure performing (2 × 2) tunnel permitting K⁺ insertion and had a nanorod morphology. The Fe ion that was doped into MnO₂ caused a phase transformation from α-MnO₂ to Ramsdellite R-MnO₂ after x = 0.15 was reached and the tunnel dimension changed to (2 × 1). Furthermore, this caused increased micro-strain and oxygen vacancies. An oxidation state analysis of Mn and substituted Fe in the octahedron sites found mixed 3+ and 4+ states. Electrical characterization revealed that the conductivity of Fe-doped MnO₂ is potentially electron influenced by the oxidation state of the cations in the octahedron sites, the micro-strain, the dislocation density, and the movement of K⁺ ions in the tunnel.

Phase transformation from initially α-MnO₂ to R-MnO₂ due to Fe-doping cause modification of interatomic distances affects to the electrical properties.

Structure properties and dielectric relaxation of Ca0.1Na0.9Ti0.1Nb0.9O3 ceramic

In this paper, the synthesis of Ca_0.1Na_0.9Ti_0.1Nb_0.9O₃ (CNTN) ceramic by a solid-state reaction method is reported. The results of Rietveld refinement of X-ray diffraction (XRD) patterns at room temperature showed a pure tetragonal perovskite (P4mm space group). Raman spectroscopy analysis, ranging from of 50 to 1000 cm⁻¹, at room temperature, validates the results of XRD. The dielectric properties was studied by complex impedance spectroscopy examined in broad frequency range, 100 Hz to 200 kHz, at different temperatures. The dielectric permittivity for our CNTN compound confirms the typical relaxor behavior. The investigation of the diffuseness of the transition was conducted by fitting the experimental data with modified Curie–Weiss law; Gaussian distribution and Power law confirm the presence of a short-range association between the polar nanoregions (PNRs). The obtained values of the diffuseness coefficient are of the order 1.6, which corresponds to the diffuse phase transition (DPT) ascribed to the existence of various states of polarization, thus various relaxation times in different regions. The value of diffuseness is of the order 85 and the degree of relaxor (ΔT_cm = 65 K) is interesting as far as microelectric applications are concerned. Moreover, based on the frequency dependence of temperature at dielectric maxima using Vogel–Fulcher relationship, a strong evidence for a static freezing temperature with regards to thermally-activated polarization fluctuations was found.

In this paper, the synthesis of Ca_0.1Na_0.9Ti_0.1Nb_0.9O₃ (CNTN) ceramic by a solid-state reaction is reported. The results of Rietveld refinement of X-ray diffraction patterns at room temperature showed a pure tetragonal perovskite (P4mm space group).

A monoclinic to tetragonal crossover in (Na0.5Bi0.5TiO3)(1−x)(BaZrO3)xceramic: a lead-free ferroelectric material

A single-phase solid solution of Na0.5Bi0.5TiO3(NBT) and BaZrO3(BZ),i.e.(NBT)(1−x)(BaZrO3)x(x= 0.00, 0.01, 0.03, 0.05 and 0.07), was synthesized using the solid-state reaction method. It is found that the temperature for single-phase formation increases with increasing BZ content. A detailed structural investigation was carried out as a function of composition using Rietveld analysis of powder X-ray diffraction data. The structural refinement reveals a crossover from monoclinic (Cc) to tetragonal (P4mm) symmetry in the composition range 0.03 <x< 0.05. The intensity of superlattice reflection due toa−a−c−tilting of oxygen octahedra in theCcphase was found to decrease with increasing BZ content. The unit-cell volume was also found to increase with BZ content, which was attributed to the higher ionic radii of Ba2+and Zr4+in comparison to Bi3+(Na+) and Ti4+. The structural phase boundary observed in (NBT)(1−x)(BaZrO3)xis concurrent with the observation of morphotropic phase boundary like behaviour.