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This work compares the dielectric properties of two new materials. One was 0.88 bismuth manganite–0.12 lead titanate (noted BM–PT hereafter) ceramics composite obtained by standard high-temperature sintering. The second composite was obtained from powdered ceramics dispersed in epoxy glue (noted BM–PT–epoxy). The occurrence of four phases in the ceramics, using X-ray powder diffraction (XRD), was recognized: orthorhombic Pbam, cubic Pn 3 ‾ m, cubic Pm 3 ‾ m, and monoclinic P2/m phase. Pseudo-Voigt function fitting confirmed significant structural disorder in the BiMn2O5 crystal lattice. Analysis of broadband dielectric spectroscopy data confirmed the applicability of the small polaron model to explain detected relaxation processes. Involvement of oxygen vacancies in relaxation and their correspondence to ordered, uniform potential wells in crystal lattices was deduced. Electric conductivity relaxation times behavior proved the sensitivity of the ceramics’ electrical features to hydrostatic pressure. BM–PT–epoxy composite exhibited dielectric permittivity and losses two orders of magnitude lower than those of BM–PT ceramics that opened new prospects to application. One relaxation process in BM–PT–epoxy composite related to the ceramics fill contribution. Other induced relaxation, observed only in this composite, was attributed to interactions at interfaces between the introduced powdered ceramics and the epoxy glue matrix. We showed that stresses generated either by hydrostatic pressure or through the interfacial interaction of epoxy matrix led to the same results: relaxation times shortening.

Thermodynamic studies of a single crystal lead titanate (PbTiO3) doped with manganese (Mn) under equilibrium conditions by the method of Knudsen Effusion Mass Spectrometry (KEMS) were conducted in the temperature range 950–1250 K. The vaporization of pure PbO(c) was investigated at temperatures of 810–1040 K. The ferro-paraelectric phase change at 763 K is supposed to be classified as a continuous transition. The thermodynamic activity lead oxide was higher in a Mn-doped PbTiO3 (stability was lower than in pure PbTiO3). Titanium (Ti) was replaced by manganese (Mn) in the perovskite structure within the solubility range, and lead (Pb) was certainly not replaced. PbTiO3:Mn(c) showed long-term stability nearby the ferroelectric-paraelectric phase transition. The ferroelectric-paraelectric phase transition at 763 K is supposed to be classified as a continuous transition.

Structural, dielectric and magnetic properties of nano-size polycrystalline, La2CuMnO6 (LCM) samples were studied in the temperature range 80 K to 300 K. Orthorhombic single phase with space group 'Pnma' was confirmed by Rietveld refinement of XRD peaks. The small-polaron driven dielectric dispersion showed relaxation peaks in the vicinity of low-temperatures. The X-ray absorption spectroscopy (XAS) confirmed the charge states of Cu (2+) and Mn (4+) ions. DC-resistivity analysis supported the thermally activated conduction for high temperature and the variable range hoping (VRH) mechanism of conduction at low-temperature. The deviation of super-exchange angles between B-site cations from an ideal 180º value produced non-collinearity in the antiferromagnetic response of this ceramic and was confirmed canted antiferromagnetic behaviour. Positive Curie temperature along with finite coercivity indicated that the super-exchange interaction between Cu2+ and Mn4+ ions influenced the magnetic behaviour of this ceramics and showed a heterogenous magnetic response.

This report documents the electrical features of (1-x) Pb(Zr0·70Ti0.30)O3–x BiMn2O5 ceramics with x = 0–0.05 (PZT–BM). A structural disorder was introduced by doping with non-polar bismuth manganite (BM) to increase the chemical disorder in PZT ceramics, which is one of the reasons for its marked piezoelectric properties. The chemical disorder was confirmed using scanning electron microscopy. The rhombohedral symmetry of a crystal lattice was determined using the XRD powder test. To assess the influence of BM dopant on the electric properties of PZT, dielectric spectroscopy was performed at a frequency f = 1 kHz–1 MHz and in a temperature range of 290–680 K. Several effects on the dielectric characteristics were induced by the addition of BM, including the shift and diffuseness of the transition from the ferroelectric to the paraelectric phase and the diffuseness of the transition between two ferroelectric phases. The electrical conductivity increased as the BM content increased. Piezoelectric studies have shown that 0.99 PZT–0.01 BM ceramics exhibit better piezoelectric properties and higher permittivity than pure PZT ceramics. The 0.99 PZT–0.01 BM piezoelectric coefficient d33 increased by approximately 30% compared with pure PZT.

Results of broadband dielectric/electric investigations of Bi(Mn0.33Nb0.67)O3.1 ceramics are presented in wide frequency range 20 Hz–3 GHz. The electric properties of Bi(Mn0.33Nb0.67)O3.1 ceramics ...

Ceramics based on lead zirconate-titanate Pb(Zr0.70Ti0.30)O3 (PZT), bismuth manganite (BM) and the composite (1 − x) PZT–x BM were obtained. A systematic study of linear and nonlinear dielectric susceptibilities temperature and frequency dependences was conducted. A composition-induced crossover in nonlinear dielectric susceptibility was detected. The so-called scaled nonlinear susceptibility, a3, was obtained from experimental values of the real part of the linear and third-order nonlinear dielectric susceptibilities. The value for a3 was negative for low BM content in the whole temperature range specific to discontinuous ferroelectric phase transitions and relaxor behavior. In contradiction, a3 was positive for BM and for the composite with sufficiently high BM content. The positive a3 was attributed to a subsystem of dipoles created by trapped charges. Hopping charge transfer, which is a dominant mechanism for conduction in manganites, is responsible for the positive a3 and for the colossal magnitude of the imaginary part of the linear dielectric susceptibility. The concentration of the ions was determined using scanning electron microscopy. The chemical disorder and the precipitation of ions determined using time of flight–secondary ion mass spectrometry correspond to a crossover in the electrical features.

Double perovskite La2CrMnO6 ceramics was sintered using standard high temperature route in ambient air. The orthorhombic Pbnm cell characterized by a total disorder between Cr and Mn ions was determined using an XRD powder test. The grain morphology, porosity and chemical composition were determined using scanning electron microscopy. The X-ray photoemission spectroscopy showed several contributions to O 1 s, La 3d, Mn 2p, and Cr 2p core lines related to the occurrence of multiple ionic states. The electrical permittivity, modulus, AC and DC conductivity were measured in ranges of f = 20 Hz – 1 MHz and 76–440 K. The electrical transport mechanism was attributed to the small polarons. The nearest neighbor hopping occurred in the range 170 to 440 K. The variable range hoping, attributed to the Fermi glass features and disorder, was detected in the range 100 to 160 K. The relaxation process related to the temperature-independent activation energy was deduced from the electric modulus scaling.

The electrical, magnetic, and structural features of bismuth manganite (BM), e.g., BiMnO3, and bismuth ferrite (BF), e.g., BiFeO3, are reviewed. Induced multiferroicity and enhanced magnetoelectric coupling are required for various modern device applications. BM and BF were synthesized using standard high-temperature sintering and processes such as sol–gel, hydrothermal, or wet chemical methods combined with annealing. The size and morphology of the nanoscale particles were controlled, although they were usually inhomogeneous. BF exhibits structurally stable antiferromagnetic (AFM) and ferroelectric (FE) phases in wide temperature ranges. Ferromagnetic (FM) order was induced in a thick shell around the AFM core of the nanoscale BF particles, which was attributed to a size effect related to surface strains and disorder. BM exhibited both structurally stable and unstable phases. The BiMnO3, Bi12MnO20, and BiMn2O5 structures are nonferroelectric. The perovskite BiMnO3 form was synthesized under high hydrostatic pressure. FM order occurs in BM at low temperatures. Bi(MnFe)O3 solid solution samples exhibited competition between AFM and FM ordering. Doping can decrease the content of unavoidable secondary phases. Doping in the Bi ion sublattice can stabilize the crystal lattice owing to local strains caused by the difference in ionic radius between Bi and the dopant. Doping in the Fe and Mn sublattices affects the electrical features. The main achievement of substitution with tetra- and pentavalent ions is compensation of the oxygen vacancies. In turn, leakage current suppression enables switching of FE domains and polarization of the samples. A significant enhancement of magnetoelectric coupling was observed in composites formed from BF and other FE materials. The leakage currents can be diminished when an insulator polymer matrix blocks percolation. The potential applicability is related to enhanced magnetoelectric coupling. The constructed devices meet the size effect limitations for FE and FM ordering. Resistive switching suggests possible use in nonvolatile memories and gaseous sensors. The sensors can be used for hydrophones and for photovoltaic and photoluminescence applications, and they can be constructed from multiphase materials. Bulk multiferroic solid solutions, composites, and nanoheterostructures have already been tested for use in sensors, transducers, and read/write devices for technical purposes.

The (1 − x)Pb(Zr0.70Ti0.30)O3–xBiMn2O5 ceramics (PZT-BM), where x = 0, 0.02, 0.055, 0.11, 0.15, 0.22 and 1, were studied. We determined how addition of nonpolar BM influenced electrical properties of the ferroelectric PZT ceramics. Impedance spectroscopy measurements in broad frequency and temperature ranges were performed and several contributions to impedance response were identified. A crossover to the relaxor state was observed in the PZT-BM ceramics by doping with Bi and Mn ions. The relaxation times for the electric conductivity relaxation and dipole relaxation were estimated from electric modulus representation of the data. Activation energy values of the conductivity process, estimated for T > 510 K, decreased from 0.82 to 0.37 eV when BM content increased. The occurrence of the high-frequency dipole relaxation was assigned to the charge transfer of Ti3+/Ti4+, Zr3+/Zr4+ and Mn3+/Mn4+ ions. Occurrence of the ferroelectric relaxor features were deduced from the non-Arrhenius dependence of the relaxation times. Superposition of the relaxor features and electric relaxations provides high value permittivity (e′ > 1000) in wide temperature range (~ 250–573 K). This effect corresponds to the disorder and precipitation of ions that were shown using x-ray photoelectron spectroscopy and the time of flight–secondary ion mass spectrometry.

Electrical properties of composite consisted of epoxy-glue and powdered bismuth manganite Bi12MnO20–BiMn2O5 ceramics were studied. Samples contained 66 wt% of bismuth manganite. Secondary electron images and backscattered electron images were collected for the epoxy-glue and the epoxy-glue/bismuth manganite samples. Microanalysis shown that majority of bismuth manganite powder was homogenously distributed in epoxy-glue matrix. Lack of changes in crystallographic structure, in 300–450 K range, was deduced from the X-ray diffraction patterns. The electric impedance was measured at radio-frequencies. It was analysed using electric permittivity ɛ*( T, f ) and modulus M″(T, f ) representation. Epoxy-glue/bismuth manganite composite exhibited, at room temperature, conductivity, σ( f ) = 10−5 to 10−7 S m−1, permittivity, ɛ′≈10, losses, tan δ = 0.2–0.8 and dispersion markedly lower than bismuth manganite ceramics. Electric relaxation was induced in epoxy-glue/bismuth manganite composite samples. The Vogel–Fulcher–Tammann equation was fitted to relaxation times temperature dependence, obtained from M″(T, f ). The estimated values of Vogel–Fulcher equation parameters were frequency f0 = 2.2 × 108 Hz, energy UT = 1050 K and glass transition temperature Tg = 282 K. The relaxation times were attributed to strains, which would occur at interfacial layers between the bismuth manganite grain and the polymer matrix.

Effects of doping on ABO 3 perovskite PZT compounds were studied. We determined effects of doping with Na ions (0.5–2.5 at.%) in A sublattice of Pb(Zr,Ti)O 3 and (Pb,La)(Zr,Ti)O 3 ceramics. The phase transition between ferro- and paraelectric phase was shifted, the dielectric losses decreased, and the piezoelectric coefficients, K p and d 33 , were improved. The properties of bismuth manganite doped to PZT ceramics, (1- x )PZT-( x )BiMn 2 O 5 ( x = 0.055, 0.11), were studied. The effects of Bi doping in A sublattice and Mn doping in B sublattice were determined. The PZT-BiMn 2 O 5 formed a composite of two solid solutions, one the ferroelectric rhombohedral R3m phase related to PZT, and the orthorhombic Pbam phase originated from bismuth manganite. Composition was estimated by using the scanning electron microscopy. Electrical impedance was measured in 100 Hz–1 MHz and 85–705 K ranges. Two types of the relaxations, manifested in the impedance spectra, were determined. One was attributed to charge transfer in B sublattice and/or polaronic mechanism. Second was fitted by using Vogel-Fulcher law that verified relaxor-like state for 0.89PZT-0.11BiMn 2 O 5 compound. The epoxy-glue/bismuth-manganite composite was obtained. Vogel-Fulcher law confirmed glassy features for this material. Effective role of 0-3 connectivity in suppression of dielectric losses and transient currents was verified.

Ferroelectric (Ba0.83Ca0.17)TiO3 ceramics was sintered by the solid state reaction method. The material was sintered in three steps that allowed remarkably modifying structure and electrical features important from an application point of view. Major tetragonal phase of the material was detected using X-ray diffraction study. The scanning electron microscope test showed fluctuation in chemical composition. The ferroelectric to paraelectric phase transition was diffused and markedly shifted to lower temperature, TC = 339 K, respectively to barium titanate. Moreover, it showed the pressure sensitivity dTC/dp = −37 K/GPa. These effects were attributed to local disorder both in Ba/Ca and Ti sublattices. The high magnitude dielectric permittivity, e′~1000–2000, was observed in 200–400 K temperature range. The net polarization, which was estimated from the pyroelectric effect, decreased from ~3 µC/cm2 to zero in ~100–400 K range. The ceramics displayed the piezoelectric coefficient, d33 = 58 pC/N, the spontaneous polarization, PS = 11–14 µC/cm2, the remnant polarization, PR~2 µC/cm2, the coercive field, EC~1.5–3 kV/cm, and the energy density storage efficiency factor, ξ ≈ 33%, at room temperature.

The composite 0.96 BM–0.04 PT ceramics was sintered from non-polar bismuth manganite (BM) and ferroelectric lead titanate (PT) components. We show influence of small amount of PT on structure ordering of BM. The X-ray pattern analysis showed occurrence of three phases: orthorhombic Pbam related to BiMn2O5, cubic P n 3 ¯ m attributed to δ−Bi2O3, and tetragonal P 4 ¯ 2 1 c related to unrecognized phase Bi20TiO32 isostructural to β−Bi2O3. Occurrence of these three phases reflected in variation in chemical compositions detected using transmission electron microscopy. Correspondence between nano-structural features of BM-PT and electrical relaxation processes was studied. The DC resistivity temperature dependence exhibited crossover from variable range hopping to nearest-neighbor hopping of small polarons. Furthermore, three electrical relaxations attributed to small polaron hopping were distinguished. Two relaxations corresponded to BM-originated phases. One relaxation exhibited crossover from variable range hopping to nearest-neighbor hopping of small polarons. Second relaxation showed crossover from variable range hopping to Vogel-Fulcher temperature dependence. Third relaxation, related to nearest-neighbor hopping of small polarons, was attributed to Bi20TiO32:Pb phase derived from PT compound. Structural disorder of BM-PT phases reflected in Fermi glass features manifested by variable range hopping of polarons. Moreover, we showed sensitivity of BM-PT ceramics on high hydrostatic pressure. Applied hydrostatic pressure, p = 800 and 1600 MPa, shortened the relaxation times. We propose equation of state for relaxation process related with PT amount doped to BM ceramics. Equation of state of dielectric includes response to varied hydrostatic pressure and temperature, that is to different thermodynamic conditions. Correspondence between effects of applied hydrostatic pressure and presumed chemical pressure was considered as consequence of inter-diffusion of Pb, Bi, Mn, and Ti ions and their mutual substitution.

Bismuth manganite ceramics, consisted of two phases: cubic I23 and orthorhombic Pbam, were obtained by high-temperature sintering in the air. The powdered ceramics were sintered in gaseous nitrogen flow at stabilized temperature of TS = 870–1120 K for 4 h. Grain structure and chemical composition were checked by scanning electron microscopy (SEM). We observed changes in the grain shapes, the number and size of the hexagon-based parallelepipeds increased. The X-ray diffraction (XRD) test has shown that the orthorhombic BiMn2O5 phase formation was favored. The local disorder was tested by X-ray photoemission spectroscopy. Multi-component lines assigned to O 1s, Mn 2p, Bi 4f were detected. The ratio of intensities of particular components was influenced by the sintering conditions. The shape of valence band was not influenced by the sintering conditions. Electric resistivity was measured in 200–750 K range with the use of Ag and In electrodes. The activation energy increased slightly when the sinteri...

We sintered the new (1 − x )Pb(Zr 0.70 Ti 0.30 )O 3 – x BiMnO 3 ( x = 0, 0.055, and 0.11) ceramics. The XRD test has shown the rhombohedral R3m symmetry for the PZT sample. The (1 − x )PZT– x BiMnO 3 samples show the existence of two phases, the one with R3m and the second with orthorhombic Pbam symmetry. Scanning electron microscopy test have shown a lack of bismuth oxide and manganese oxides precipitation. The density of states was calculated for a 40-atom supercell which corresponds to (Pb 7 Bi)(Zr 4 Ti 3 Mn)O 24 and (Pb 7 Bi)(Zr 3 MnTi 4 )O 24 ceramic compositions. The dielectric spectroscopy was conducted for f = 100 Hz–1 MHz in the 85–705 K range. The electric permittivity test indicated the existence of PZT phase within the PZT–BiMnO 3 ceramics. The addition of BiMnO 3 caused dispersion of electric conductivity in the low temperature range and induced a relaxor state in the high temperature range.

Bismuth manganite ceramics has been obtained by high temperature sintering in air. It was found from the X-ray diffraction pattern analysis that the ceramics consists of two centrosymmetric phases: the cubic I23 and the orthorhombic Pbam. Impedance has been measured at radiofrequencies in 85–500 K range. Two relaxation processes have been discerned. One process, which shows characteristic time value τ0 ≈ 10−12 s, occurs in 120–230 K range and it has been assigned to polaronic conductivity. The other process occurs in 270–310 K range and it exhibits longer characteristic time value τ0 ≈ 10−8 s. The resistance Rdc(T) temperature dependence shows semiconductor features with activation energy Ea = 0.28–0.40 eV for the as-sintered samples. The semiconductor to metallic-type transition has been induced after electroformation procedure carried out at 790 K in ambient air. We propose that extended defects, related to occurrence of the two phases, facilitate resistive switching.

Five phase transitions were observed in NaNbO3 ceramics on cooling by broadband (20 Hz-1 GHz) dielectric investigations in temperature range from 25 K to 1000 K. Despite that T1-T2 and S-T1 phase transitions are non polar, they are clearly expressed in dielectric properties of ceramics due the corresponding conductivity anomalies. At higher temperature (above 600 K) the electrical conductivity dominates in the dielectric spectra of ceramics. The electrical conductivity increases after annealing and have peculiarities close to T1-T2, S-T1, P-R phase transitions temperatures. Two dielectric dispersion processes, at low temperatures (in N phase below 120 K) with very low activation energy and freezing temperatures values, are assigned to domains dynamics.

Thermodynamic studies of a polycrystalline sodium niobate (NaNbO 3 ) under equilibrium conditions by the method of Knudsen effusion mass spectrometry (KEMS) were conducted in the temperature range 1250–1485 K. The vaporization of pure Na 2 O(c) was investigated at temperatures of 900–1165 K. Thermodynamic quantities of sublimation enthalpy, activity, and entropy were derived from the partial pressures of gaseous Na, Na 2 O, and O 2 over the sodium niobate and pure sodium oxide reference samples. The sublimation enthalpy of Na from NaNbO 3 (c) at T =1370 K was Δ sub H 1370 K 0 ( Na ) = 465 ± 9 kJ mol − 1 . Heat capacity measurements under constant pressure ( C p ( T ) 0 ) by Dynamic Scanning Calorimetry (DSC) in the temperature range 298–1450 K resulted in six polynomial equations for each branch of the five transitions. Below the first phase transition at 639 K the C p ( T ) 0 values increased from 97 to 123 J mol −1 K −1 . Beyond this transition and up to the third one at 792 K, C p ( T ) 0 gently inclined from about 120 to a maximum value of 123 J mol −1 K −1 . Finally, beyond the fifth transition at 907 K it approximated to an almost constant value of 115 J mol −1 K −1 . The enthalpy and the entropy values were calculated from the C p ( T ) 0 polynomials and from the vaporization studies. The enthalpy of the five transitions in sodium niobate, Δ trs H 298 0 ( NaNbO 3 ( c ) ) were measured by drop calorimetry. Deduced from empirical and experimental approaches, the heat of reaction for oxides was Δ r H 298 0 ( NaNbO 3 ( c ) ) = − 94.3 ± 7 kJ mol −1 and the heat of formation was Δ f H 298 0 ( NaNbO 3 ( c ) ) = − 1250.8 ± 7 kJ mol −1 . The thermodynamic activity of Na 2 O in sodium niobate was temperature dependent, and its values varied from 2.6×10 −3 to 8.3×10 −4 in the range 1100–1250 K. NaNbO 3 (c) has a long-term stability in the temperature range including the transition to cubic phase at 907 K.

Fe-doped Bi12MnO20–BiMn2O5 ceramics was sintered at 1130 K for 6 h in ambient air. Two centro-symmetric phases formed thermodynamically stable self-composite material that was deduced from X-ray pattern analysis. The lattice parameters were a = 10.147(8) Å—for the cubic I23 Bi12MnO20 phase; and a = 7.545(4) Å, b = 8.538(1) Å, c = 5.758(3) Å—for the orthorhombic Pbam BiMn2O5 phase. The 57Fe Mössbauer spectrum, recorded at room temperature, has shown pure electronic quadrupolar split. The major doublets reflected the occurrence of Fe3+ ions distributed in two sites, i.e., octahedral Fe4+O6 and square pyramidal Fe3+O5, with preferential occupation of the pyramidal sites, that was consistent with the Pbam phase symmetry. The third doublet resulted from the presence of iron Fe3+ in tetrahedral Fe3+O4 coordination and corresponded to a small admixture of the I23 phase. The DC resistivity ρDC(T) dependence on temperature has shown thermally activated features, and the value of Ea,DC varied in the range of 0.22–0.37 eV. The electric impedance was measured in the f = 20 Hz–1 MHz and 100–690 K range. Two electrical relaxations were determined using the electric modulus formalism M″(T). Low-temperature relaxation has shown the temperature-dependent activation energy EA,1 = 0.14–0.20 eV and characteristic time values of τ01 = 10−10–10−12 s in 100–200 K range. It was attributed to the charge transfer between Mn4+/Mn3+ sites. The other relaxation occurred in the 170–220 K range, and it exhibited the following values: τ02 = 10−11 s, and EA,2 = 0.27 eV. A disorder-related VRH polaron model was proposed for ρDC(T) and for electric relaxation processes., Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

In this paper, the resistance switching effect has been studied in NaNbO3:Mn crystals. Samples were rejuvenated in ambient air, below and above antiferroelectric phase transition. Dielectric spectroscopy has exhibited weak dispersion. The influence of annealing on the electronic structure has been determined with the use of X-ray photoelectron spectroscopy. Na2s, Nb3d, O1s, and Mn2p lines of the aged as-grown crystal and the rejuvenated samples spectra have been analyzed. Nb4+ states observed in the samples point to the presence of oxygen vacancies in the surface layer. Na ions migrate toward the surface due to rejuvenation. Switching from an insulator high-resistance state to a semiconductor medium resistance and finally to a metallic-type low-resistance state has been observed. The results are discussed within the framework of the extended defects model. We propose that the aliovalent Mn2+ dopant ions stabilize the oxygen vacancies and enable the resistive switching.

Thermodynamic studies of a single crystal lead titanate (PbTiO3) under equilibrium conditions by the method of Knudsen effusion mass spectrometry (KEMS) were conducted in the temperature range 950–1210 K. The vaporization of pure PbO(c) was investigated at temperatures of 810–1040 K. Thermodynamic quantities of sublimation enthalpy, activity, and entropy were derived from the partial pressures of gaseous Pb, PbO, and O2 over the lead titanate and pure lead oxide reference samples. The sublimation enthalpy of Pb from PbTiO3(c) at T=1080 K was ΔsubH1080K0(Pb)=(340±11)kJmol−1 and for PbO was ΔsubH1080K0=(251±12)kJmol−1. Heat capacity measurements under constant pressure (Cp(T)0) by dynamic scanning calorimetry (DSC) in the temperature range 298–1273 K resulted in two polynomial equations. The Cp(T)0 values increased from 106 to 139±0.2J mol−1 K−1 below the ferroelectric–paraelectric phase transition at Tc=763 K, and Cp(T)0≅(112±0.3) J mol−1 K−1 was almost constant above Tc. The low values of entropy, ΔtrsS=(2.1±0.9) J mol−1 K−1 and enthalpy, ΔtrsH=(1.57±0.7) kJ mol−1, and the λ (lambda)-shape of the ferro-paraelectric phase change in the Cp(T)0 function suggest that the transition can be classified as a first order one with a tendency to a continuous one. The enthalpy and the entropy values were calculated from the Cp(T)0 polynomials and from the vaporization studies. Deduced from empirical and experimental approaches, the heat of reaction was ΔrH2980(PbTiO3(c))=−(26.4±1.8)kJmol−1 and the heat of formation was ΔfH2980(PbTiO3(c))=−(1190.4±3.9)kJmol−1. The thermodynamic activity of Pb and PbO in lead titanate was temperature dependent and their values were a=(8.67±2.9)10−4, and (9.96±3.6)10−3, respectively, at a temperature of 1000 K. Near the ferroelectric–paraelectric phase change at 770 K, PbTiO3(c) has a long-term stability.

PbTiO3 powder has been obtained by the hydrothermal method. The studied ceramics has been sintered from powder. SEM analysis exhibited stoichiometric composition. XRD analysis of the reference crystal, the hydrothermal powder as well as the ceramics samples has shown the tetragonal symmetry P4 mm. The size of the crystallites in the powder grain varied from 14 to 22 nm. The size of the crystallites decreased by 30% whereas the size of grain increased after sintering the powder to the ceramics form. The sintering process increased the shift of ions from the general position and increased disorder. Electric conductivity exhibited semiconductor features.

The as-grown aged and thermally annealed at 720 K and 820 K PbTiO3 crystals were prepared. The ɛ′(T,f) and σAC(T,f) were measured at radio frequencies. Samples heated at 720 K shown resistive switching to metallic-type σAC(T). The resistivity switching was confirmed by RDC(T) measurement. The samples annealed at 820 K were rejuvenated, exhibited Curie-Weiss dependence above TC = 750 K and semiconductor conductivity. Annealing induced changes in shape of the Pb 4f, Ti 2p, O 1s, and VB XPS lines. We propose a model related to ionic migration toward FE domain walls and to vortices which provide conducting channels.

Proton exchange reaction (Li+/H+) was carried out on LiNbO3 crystals (z-cut). Reaction was conducted in concentrated environment of HNO3, at stabilized temperature 110°C. Portion of acid was added after each 24 h interval. The reference LiNbO3 crystal sample and etched for 240 h HxLi1−xNbO3 crystals were used for surface sensitive studies. SIMS test proved that H and Li the proton exchange reaction took place. Electronic structure was checked by XPS. The Li, Nb, O core lines, and VB line were analyzed. Substitution of Li by H ions deformed shape of the XPS lines that indicated crystal structure change.

In our study BiMnO3 ceramics has been sintered. The X-ray diffraction test has shown that the crystal lattice symmetry is monoclinic and centrosymmetric. Grain structure and stoichiometry has been determined by scanning electron microscopy whereas local disorder by X-ray photoemission spectroscopy. Leakage currents dominated the D–E hysteresis loop. Electric conductivity has been measured in the 85–770 K range. The studied fresh ceramics shows semiconductor properties. Charge-order transition occurrence has been deduced. The dc resistance switching occurs following the application of electroformation at a high temperature range. This effect is reversible, i.e. the Rdc(T) recovers semiconductor properties after thermal and electric field treatment.

Results of broadband dielectric/electric investigations of (Na0.5Pb0.5)(Mn0.5Nb0.5)O3 ceramics are presented in wide frequency range 20 Hz–3 GHz. The electric properties of (Na0.5Pb0.5)(Mn0.5Nb0.5)O3 ceramics are mainly governed by high ionic conductivity. One ionic and three polaronic contributions to electrical conductivity were successfully separated by employing impedance formalism.

(Bi1/2Na1/2)(Mn1/2Nb1/2)O3 (BNMNO) ceramics were sintered at ambient air. XRD test exhibited coexistence of phases. The permittivity and conductance were measured at radio frequencies. Activation energy values were estimated as 0.38 eV. Electronic structure was simulated for BNMNO and also for BiMnO3 (BMO) as the reference. The ab initio calculations were performed within DFT using LCAO with localized basis set in the form of spherical functions as implemented in the SIESTA 3.0 code together with a spin polarization. An energy gap was estimated for the ideal BMO and BNMNO lattice to be 0.8 eV and 0.4 eV, respectively. An oxygen vacancy and an interstitial oxygen introduced to calculation caused narrowing the gap.

The PbTiO 3 crystals aged during 24 years were annealed in ferroelectric phase at 720 K and in paraelectric phase at 820 K. The reference fresh ceramics were sintered from powders obtained by hydrothermal growth. The resistive switching to metallic-type dependence occurred in the crystal samples annealed in ferroelectric phase. The other samples, i.e. aged crystals, crystals annealed in paraelectric phase, and ceramics exhibited semiconductor features. The electric conductivity relaxation was related to defects. Electronic structure was tested by XPS. The annealing changed contributions from various charge states of Pb, Ti, and O ions. The conditions for the resistive switching were discussed in accordance to literature models, which concern defects drift and occurrence of conductive channels along vortices formed by ferroelectric domains.

Ferroelectric properties of BaTi1− x Hf x O3 ceramics with Hf content x = 0, 0.001, and 0.025 were examined. It was found that the substitution of Hf4+ for Ti4+ in BaTiO3 resulted in shifting the two low-temperature transitions (T 1, T 2) of the investigated samples to higher temperatures and decreasing the tetragonal-cubic phase transition temperature (T c). This is a well-known pinching effect. Thermal parameters of the transitions, such as the enthalpy ΔH and the entropy ΔS, were also estimated and discussed.

In the study we present results on topography, morphology, chemical composition, electronic structure and electrical properties of the (100) surface layer of KTaO3 single crystal caused by sputtering with Ar+ ion beam with energy of 1 keV. Several surface sensitive techniques, i.e. X-ray photoelectron spectroscopy (XPS), local conductivity of atomic force microscopy (LC-AFM), and Kelvin Probe Force Microscopy (KPFM) were used. The observed changes in the electronic structure were explained as a result of the chemical decomposition of the surface layer. A correlation between the electronic states which appeared in the energy gap and the changes in charge state of Ta ions was found. The activation energy related to averaged local conductivity temperature dependence was estimated from Arrhenius plot. It was also found, that variations in the local contact potential difference (LCPD) indicated changes in the chemical composition in nano-scale. The chemical reconstruction of the KTaO3 surface modified by Ar+ ion beam was deduced. This non-homogeneity corresponded to 2-D non-homogeneity of the local electric conduction (LC-AFM), which occurred within nano-areas after sputtering. Chemical reactivity of the modified surface with CO2 and O2 was observed. The reversibility of the Ar+ induced loss of oxygen non-stoichiometry was observed after the sample was exposed to various doses of O2. The successful reversibility occurred after oxidation process at high temperature, i.e. 300 °C.

The chemical bonding of Mn atoms in (Na1-xBix)(Nb1-yMny)O3 ceramics were analysed using the X-ray Absorption Near Edge Structure (XANES) measurement at the Mn L3,2–edge. In all the compounds coexistence of the covalent bonding MnCV state and ionic Mn+k states was found. The increase in the Bi and Mn content caused the marked dispersion and increased the values of electric conductivity and dielectric permittivity of the ceramics.

The process of ionic segregation in the surface layer induced by the thermal treatment of the NaNbO3 crystal was studied. The study of the as grown crystal and the crystal heated at 970 K in ambient air was carried out for comparison. The changes in the concentration of the elements within the surface layer were determined using XPS measurements. The AFM technique was applied to determine the surface morphology related to nano-scale transformation. The possibility of appearance of the Ruddlesden–Popper phases was detected by the XRD test. The change in the features of the electric permittivity, the loss tangent, and the electric conductivity was ascribed to the marked participation of the chemically modified surface layer in the measured effective electrical properties.

The X-ray diffraction patterns of (Na2/3Pb1/3)(Mn1/2Nb1/2)O3 ceramics were measured within 15–850 K temperature range. The anomaly in the thermal expansion temperature dependence occurred in 250–365 K range. The generalised Cole–Cole model was proposed to describe the measured effective electric permittivity influenced by high electric conduction and the coexistence of two contributions ɛ*(T,f) = ɛ*lattice + ɛ*carriers was considered. The analysis of the electric permittivity and conduction exhibited two relaxation processes. The electric conduction relaxation characteristic time values indicated the small polaron mechanism with τ0 ≈ 10−13 s occurring in 240–345 K range and the ionic mechanism with τ0 ≈ 10−11 s involved in the other relaxation occurring in the 320–510 K range. The ionic relaxation process was ascribed to a subsystem of defects, which was weakly interrelated to the anomaly in thermal expansion of the (Na2/3Pb1/3)(Mn1/2Nb1/2)O3 ceramics. The Gate model was proposed to describe the ionic relaxation mechanism.

On the basis of our studies it results that dielectric properties of BaBi 2 Nb 2 O 9 ceramics are sensitive to axial pressure applied. The pressure causes an increase of dispersion in the real part of dielectric permittivity ɛ ′( T , f ) and a rise in the temperature T m at which the maximum in ɛ ′( T , f ) dependence occurs. The applied pressure induces in the ɛ ′( T ) dependence an additional step-like anomaly, which appears at the temperature T A T m . The applied pressure shifts both T m and T A at the same rate, i.e. d T A /d X = d T m /d X = +14 °C/kbar at high axial pressure range, above the threshold pressure X thresh . The Vogel–Fulcher relationship is employed to determine the axial pressure influence on relaxor properties of BBN ceramics. The simulated order parameter q takes non-zero values below Burn‘s temperature T B , where the polar clusters appear on cooling. For pressures higher than 0.8 kbar, the T B changes at the rate d T B /d X = −200 °C/kbar. The decrease in the difference between Burn's T B and the freezing T f temperatures induced by the applied axial pressure is observed. This could be ascribed to the narrowing of temperature range of relaxor behavior.

The results of measurement of the linear and nonlinear dielectric susceptibilities of pure and Ba-doped lead germanate, (Pb1− x Ba x )5Ge3O11 with x = 0, 0.02 and 0.05, single crystals are presented. The change in the sign of the third-order dielectric susceptibility, χ 3, as predicted by the thermodynamic theory of the continuous phase transitions, is observed in pure crystal. On the contrary, in the Ba-doped crystals, the third-order dielectric susceptibility is positive and shows a peak near the temperature, which corresponds to the position of the peak of the linear dielectric susceptibility, χ 1. This result indicates that the Ba-doped lead germanate crystals do not show features typical of a continuous phase transition. In B-doped lead germanate crystal, the scaled nonlinear sucsebtibility, a 3, shows ferroelectric relaxor-type behavior.

The transition between insulator and metal conductor states, induced by oxygen non-stoichiometry, was studied for NaNbO3 : Mn crystals. Conditions for an optimal reduction were determined on the basis of TGA tests. The temperature dependencies of the resistance measured on the macroscale showed that the transition from thermally activated to metallic features depends on the level of oxygen deficiency. The LC-AFM measurement exhibited non-homogeneous electric resistance on the nanoscale. We ascribed the local insulator–metal transition to changeover in the electronic state of the Nb ions occurring in filaments. The Mn dopant stabilised the induced oxygen non-stoichiometry and the metallic conduction down to room temperature.

New Bi(Mn 1/3 Nb 2/3 )O 3 ceramics were obtained. Their pseudo-perovskite symmetry with monoclinic distortion was determined by XRD test. Dispersion in permittivity e′ (T,f) was observed. Small polaron mechanism of electric conductivity was deduced. Several techniques were applied to evaluate electric conduction relaxation times τ(T,f) from e′(T,f), e”(T,f), tan δ(T,f), and M” (T,f) dependences. The relaxation times τ (T,f) temperature dependence was fitted with high accuracy by Fermi glass related term τ (T,f)∼ exp[(T0/T)1/4] corresponding to variable range hopping of small polaron model. Perovskite cubic structure was determined for (Bi 1/9 Na 2/3 )(Mn 1/3 Nb 2/3 )O 3 ceramics. The E a , τ0, T 0, and electric conductivity σ values were changed by Na ions addition.

Thermal diffusivity of uniaxial ferroelectric Pb 5 Ge 3 O 11 has been measured as a function of temperature using ac photopyroelectric calorimetry. The second order ferroelectric transition has been studied in order to ascertain the mechanisms which could explain the anomaly in specific heat through the study of the inverse of the thermal diffusivity. It has been shown that Pb 5 Ge 3 O 11 falls within the universality class of the mean-field model: the ferroelectric phase is very well explained within the framework of the Landau model, while in the paralectric phase a logarithmic correction must be taken into account, as predicted by renormalization group theory.

The relation between chemical composition, crystal structure and electrical features of lead germanate, (Pb5–xBax)Ge3O11, pure and doped with Ba (x = 0, 0.10, 0.25) was studied. The O deficiency and GeO2 precipitation was found in the crystals studied. In the case of the Ba-doped crystals, the XPS lines width (FWHM) variation suggests structural local disorder. The valence band is placed near 3 eV and it shows an exponential tail, which is ascribed to existence of energy levels correlated to defects. Both the valence band edge shift and the degree of disorder deduced from the change in the XPS lines width vary non-linearly with the concentration of the Ba ions. The ac conductivity activation energy values Ea = 0.55–0.85 eV indicate electric conductivity of lead germanate is determined by local energy levels originated from point defects. The analysis of the imaginary part of the electric modulus M ″(T, f) exhibited the electronic relaxation process related to electric conductivity, for which the activation energy EM = 0.63–0.72 eV, and the characteristic times τ0 of the order of 10–13 s were evaluated. The crystal structure parameters and several of the electrical conduction parameters exhibit non-monotonic dependence on the Ba concentration. It was deduced that Ba ions contributed to the mentioned phenomena by two opposite mechanisms. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Seleno-spinels with the nominal composition Cu1−xCoxCr2Se4 (for x = 0.1–0.9) and CuCr2−yCoySe4 (for y = 0.1–1.9) were prepared as polycrystalline samples using ceramic method. Change of crystal structure, from cubic to monoclinic symmetry, was observed in the first system with the increase in cobalt amount. In the second system monoclinic phase as well as single-phase CuCr2−yCoySe4 compounds were not obtained. The X-ray analysis was used in order to make phase analysis of the obtained samples to determine their crystal structure and lattice parameters. The scanning electron microscopy test confirmed the chemical composition and shown the variation in local distribution of cations. The porosity of the samples was observed. Electric resistance of the compressed powdered samples was measured at frequency 100 Hz within temperature 100–500 K range. The samples showing the spinel structure, with low Co-substitution, x = 0.1–0.5, exhibit thermally activated conductance with activation energy 90–220 meV above room temperature. The increase in the Co-concentration, x = 0.6–1.0, lowers the activation energy to about 40 meV. These samples show the metallic-type conductivity within intermediate temperature range, 200 ≲ T ≲ 400 K. The small polaron-type conductance, with low value of the activation energy, Ea ≲ 15 meV, was deduced below 300 K for the all Cu1−xCoxCr2Se4 (x = 0.1–0.9) samples. It was found that the electric transport properties correspond both to the chemical composition and to the crystal structure.