We conducted a comparative study on structural, magnetic and electric properties of MnTiO3 ceramics sintered in air (MTO-A) and nitrogen (MTO-N) to explore the impact of oxygen vacancies (OVs) on them. The X-ray diffraction patterns show that MTO-N possesses a lattice contraction induced by OVs comparing with MTO-A. Distinct spin glass (SG) with Tsg (41 K) and magnetic exchange bias (EB) are only observed in the MTO-N sample. The results indicate that OVs may well lead to the enhanced magnetization, thereby generating SG behavior. Moreover, the dielectric characteristics of MTO-A and MTO-N are investigated additionally, two disparate relaxation mechanisms of Maxwell–Wagner relaxation and OVs migration are illuminated respectively, which further support the vital function of OVs.

•Tb0.5Y0.5MnO3 ceramics are obtained by solid state reaction.•Ferroelectric transition (TC) is observed.•Two dielectric relaxations are observed in Tb0.5Y0.5MnO3 ceramics.We present here the structural and dielectric properties of Tb0.5Y0.5MnO3 ceramics synthesized by solid state reaction. The X-ray diffraction pattern shows that the sample has an orthorhombic structure with space group Pbnm. Dielectric characteristics of Tb0.5Y0.5MnO3 ceramics are investigated over a broad temperature and a frequency range. Two dielectric relaxations are observed at 40–90 and 100–220 K. The results indicate that the low temperature dielectric relaxation (LTDR) may be exhibited variable ranger hopping behavior due to the oxygen vacancies (VO+), while the high temperature dielectric relaxation (HTDR) may come from the dipolar effects associated with the charge carrier hopping between Mn2+ and Mn3+.

The ceramic TbCo0.5Mn0.5O3.07 of double-perovskite structure was prepared by solid-state reaction. Its crystal structure and magnetic and dielectric properties were investigated by first-principles calculations and experimental observations. TbCo0.5Mn0.5O3.07 possesses a monoclinic structure with P21/n space group. The c axis is the easy-magnetization axis, and it is largely caused by Co2+ anisotropy. The predominant valence states are Mn4+ and Co2+, with a small amount of Co3+ coexisting with Co2+. The ordering of Mn4+ and Co2+ results in ferromagnetic Mn4+–Co2+ interactions. Partial disorder of the B-site creates antiferromagnetic Co2+–O–Co2+ or Mn4+–O–Mn4+ interactions. The origin of metamagnetism is associated with the coexistence of antiferromagnetic and ferromagnetic phases. The magnetic exchange bias is strongly dependent on magnetic field, which is considered to be related to the metamagnetic behavior. The possibility of spin glass behavior is excluded by AC susceptibility measurements. The two observed dielectric relaxations are caused by electrons hopping between Co2+ and Mn4+ and between Co3+ and Mn4+.

•Bi occupies the Tb site in Bi-doped TbMnO3.•Bi doping alters the multiferroics of TBMO due to the strength of JTb–Tb and JTb–Mn interaction.•Bi-doping significantly depressed the dielectric constant.•The dielectric relaxor behavior at low temperature was observed.Bi doped TbMnO3 ceramics have been synthesized by solid state reaction, and the effect of substitution in TbMnO3 on the structural, magnetic and dielectric properties is investigated. The X-ray diffraction pattern shows that the samples have an orthorhombic structure. The Bi substitution is found to suppresses the Tb-spin ordering point (TTb) and ferroelectric ordering point (TC), which attributed to the strength reduction in the exchange interactions JTb–Tb and JMn–Tb. In addition, a dielectric relaxation with an activation energy of ~20 meV is observed at low temperature in Tb1−xBixMnO3, and the relaxorlike dielectric characteristics may be attributed to the dipolar effects induced by charge carrier hopping motions.

Strontium titanate films with high aa-axis orientation [a(100)=94.1%][a(100)=94.1%] and random orientation were deposited on (111) Pt/Ti/ SiO2/Si substrates by a concentration controlling of the precursor solution during the metal organic deposition process. Topography of samples was investigated by atomic force microscopy after annealing at 800 °C. X-ray diffraction found that the degree of aa-axis orientation increased with increasing annealing temperature. The leakage current and the dielectric property were strongly dependent on the film orientation, and the possible causes of orientation dependence were discussed.

Single phase ceramics CaCu3Ti4.0O12 and CaCu3Ti3.9O12 have been prepared using the traditional solid-state reaction method. Compared with the stoichiometric ceramics CaCu3Ti4.0O12, Ti-deficient ceramics CaCu3Ti3.9O12 have the larger lattice parameter, the higher force constant, and smaller dielectric constant and the lower dissipation factor, although their fundamental characters of dielectric response are similar. Their characteristic relaxation frequencies are not well fitted with the Arrhenius Law but a tentatively supposed relation. With the Cole–Cole Law, the fitted broadened factors of dissipation peaks are 0.5433 and 0.8651 for CaCu3Ti3.9O12 and CaCu3Ti4.0O12, respectively. All facts mentioned above imply that mutually correlated motion of Ti ions or defects may be expected to be responsible for the giant dielectric constant and high dissipation factor of CaCu3Ti4.0O12.

Mechanical and dielectric measurements were used to investigate the behavior of point defects and phase transition in ferroelectric ceramics. Some interesting results were obtained: (1) the dielectric loss peak in La-doped Bi4Ti3O12 was explained by the hopping of oxygen vacancies, the optimum doping content of La = 0.75 (Bi3.25La0.75Ti3O12) was discussed in terms of the competition between the density of oxygen vacancies and activation energies; (2) by use of internal friction measurements, the interaction between oxygen vacancies and ferroelectric domain walls was detected, the relationship between domain wall morphology and fatigue behavior was then well explained; (3) some internal friction peaks were also detected in SrBi2Ta2O9 and Pr(Zr0.52Ti0.48)O3 ceramics. The results mentioned above indicate that both mechanical and dielectric techniques are useful to clarify the mechanisms of ferroelectric behavior.

Yttrium substituted Bi4−xYxTi3O12 (x = 0.00, 0.10, 0.30, 0.50, 0.75, 1.00) polycrystalline thin films were synthesized by metal-organic decomposition method. Ferroelectric measurements revealed that the Bi4Ti3O12 (BTO) films substituted by Y with appropriate ratios could have higher remnant polarization and significantly improved fatigue behavior compared with BTO. The remnant polarization of the Bi3.50Y0.50Ti3O12 capacitor reached 10 μC/cm2 at an applied field about 120 kV/cm with nearly fatigue free property up to 1010 cycles. By using Raman spectra, X-ray diffraction, and scanning electron microscope to analyze the structure and composition of the films, it was found that the Y substitution of Bi at A-site induces changes in film orientation and the lattice distortion that are probably responsible for the improved ferroelectric properties. The microstructure and its relation with the leakage behavior of these thin films were also discussed.

Bi4Ti3O12 (BiT), Bi3.25La0.75Ti3O12 (BLT), Bi4−x/3Ti3−xNbxO12 (BTN) and Bi3.25−x/3La0.75Ti3−xNbxO12 (BLTN) thin films have been prepared by pulsed laser deposition. BTN and BLTN films exhibit a maximum in the remanent polarization Pr at a Nb content x=0.018. At this Nb content, the BLTN film has a Pr value (25 μC/cm2) that is much higher than that of BiT and a coercive field similar to that of BiT. The polarization of this BLTN film is fatigue-free up to 109 switching cycles. The high fatigue resistance is mainly due to the substitution of Bi3+ ions by La3+ ions at the A site and the enhanced Pr arises largely from the replacement of Ti4+ ions by Nb5+ ions at the B site. The mechanisms behind the effects of the substitution at the two sites are discussed.

Lanthanum-substituted SrBi4Ti4O15 (SBTi) ceramic SrBi4−xLaxTi4O15 (SBLT) samples were prepared by solid state reaction and their ferroelectric and dielectric properties were investigated. The incorporation of La3+ results in clear improvement for SBLT (∼0.5 and ∼0.75) on the remanent polarization for about 30% and the coercive field decreases with the increasing lanthanum content. The Curie temperature drops from 520 °C for pure SBTi to 300, 200 and 60 °C for SBLT with lanthanum content of 0.5, 0.75 and 1.0. The tangent losses reduce especially at high temperature with lanthanum substitution.

Strontium titanate films with high a-axis orientation [a(100)=94.1%] and random orientation were deposited on (111) Pt/Ti/ SiO2/Si substrates by a concentration controlling of the precursor solution during the metal organic deposition process. Topography of samples was investigated by atomic force microscopy after annealing at 800 °C. X-ray diffraction found that the degree of a-axis orientation increased with increasing annealing temperature. The leakage current and the dielectric property were strongly dependent on the film orientation, and the possible causes of orientation dependence were discussed.