CaTiO3 is a promising candidate as a pseudo-piezoelectric scaffold material for bone implantation. In this study, pure and magnesium/iron doped CaTiO3 are synthesized by sol-gel method and spark plasma sintering. Energy dispersive X-ray mapping confirm the homogenous distribution of doping elements in sintered samples. High-energy X-ray diffraction investigations reveal that doping of nanostructured CaTiO3 increased the strain and defects in the structure of CaTiO3 compared to the pure one. This led to a stronger pseudo-piezoelectric effect in the doped samples. The charge produced in magnesium doped CaTiO3 due to the direct piezoelectric effect is (2.9 ± 0.1) pC which was larger than the one produced in pure CaTiO3 (2.1 ± 0.3) pC, whereas the maximum charge was generated by iron doped CaTiO3 with (3.6 ± 0.2) pC. Therefore, the pseudo-piezoelectric behavior can be tuned by doping. This tuning of pseudo-piezoelectric response provides the possibility to systematically study the bone response using different piezoelectric strengths and possibly adjust for bone tissue engineering.

The polycrystalline perovskite calcium titanate has an orthorhombic crystal structure at room temperature, which belongs to a centro-symmetric point group. Due to this fact, it does not show piezoelectric behaviour. However, such behaviour is observed in nanostructured calcium titanate prepared by sol-gel synthesis and field assisted sintering. Whereas, the conventionally sintered sample does not show this behaviour. Presumably, the instability of regular TiO6 octahedra results in the off-centering of titanium positions of the field assisted sintered calcium titanate. This phenomenon leads to the generation of electric dipoles due to the lattice distortions produced by the formation of highly localized defects, i.e. oxygen vacancies, during densification by the field assisted sintering. As a result, pseudo-piezoelectric behaviour is observed, which confirms that the field assisted sintering triggers the piezoelectric effect but not the conventional sintering. The charge (Q) produced in the field assisted sintered sample and the piezoelectric constant (d(33)*) values have been determined to be Q = (2.1 +/- 0.3) pC and d(33+)* similar to(7.13 +/- 0.4) pm/V or d(33-)* similar to (-5.95 +/- 0.3) pm/V, respectively. This particular response of nanostructured calcium titanate is of great interest in biomedicine because it can improve the osseointegration of an implant.

This study presents a cost-efficient single-step-method to synthesize nanographite from isopropanol by bipolar pulsed electric discharges. The influence of pulse width within the nanosecond range, repetition frequency within the kilohertz range and processing time on the product was systematically investigated by Raman spectroscopy, high-resolution transmission electron microscopy and gas chromatography - mass spectrometry. It was found that long pulses in the microsecond range promote the creation of amorphous and oxidic carbon structures. Although, hydrocarbon cracking and subsequent graphitization do occur, these process conditions are not suitable to drive intermediate reduction processes. In contrast, applying short pulses in the nanosecond regime ensures fast reduction processes and formation of graphene-related nanostructures. The number of observed nanographite layers lies in the range of 3-13 with an average interlayer spacing of 3.4(0.3) angstrom and an average distance between defects of 11.5(6.0) nm meaning that the produced nanographite is in the area of small defect density. Furthermore, no significant influence of process times on the product properties over a period up to 15 min was observed, indicating good process homogeneity.

Calcium titanate has an orthorhombic crystal structure and should not exhibit piezoelectric behavior. However, in the present study such behavior is observed in nanostructured calcium titanate prepared by sol–gel synthesis and field assisted sintering. This behavior is referred to as pseudo-piezoelectricity since it is generated by distorted structure. In-situ high-energy X-ray diffraction studies have been performed to investigate this behavior. Strain and defects in the nanostructured bulk material led to its piezoelectric response with non-180° domains reorientation and domains switching under external electric field. The piezoelectric constant is comparable with the piezoelectric constants of natural bone.

Investigating the polyol-assisted synthesis of maghemite nanoflowers, a strong impact of the iron precursor stoichiometry on physical properties is found.

Fluorinated aromatic polyimide films were treated by pulse electrical discharges formed in water or isopropanol. The relative permittivity, measured in large domains of frequencies and temperatures by broadband dielectric spectroscopy, slightly decreased after plasma discharge in both types of liquids. The dipolar relaxation calculated by Arrhenius equation showed that the liquid plasma treatment decreases the rotational potential energy barrier for non-cooperative motions of dipoles, as a consequence of an increased free volume of plasma exposed films. Higher values of hardness, Young's modulus, and an improved elongation were also measured for the plasma treated samples, indicating molecular rearrangements that occur after plasma treatment.

Spark plasma sintering (SPS) is an attractive method to obtain fully densified polycrystalline ceramics at rapid sintering rates. Cerium- and yttrium-doped barium zirconate, BaZr0.7Ce0.2Y0.1O3−δ, was prepared by a SPS route, resulting in high values of density of above 98%. Investigations of microstructural and crystallographic properties with determination of grain sizes were performed by means of Scanning Electron Microscopy, X-ray Diffraction and Static Light Scattering and discussed in correlation to bulk and grain boundary conductivities obtained by AC impedance spectroscopy. Samples prepared by SPS were generally found to consist of small grains that exhibit high bulk conductivities, whereas their grain boundary conductivities were comparably small, possibly also dominated by the presence of minor phases.

In this work spinel series with the general formula Fe1-xMnxAl2O4 (where x = 0, 0.3, 0.5 and 0.7) were synthesized and characterized with respect to their structure and microstructure. X-ray diffractometry (XRD) was used to identify the phase composition that revealed a single phase spinel material. Rietveld refinements of the XRD patterns were carried out in order to determine the lattice and oxygen positional parameters of the spinel compounds. Mössbauer effect measurements were performed at room temperature to determine the local chemical environment of the Fe ions, their valences, and degrees of spinels inversion. It was shown that an increase in the Mn content led to a decrease in the ratio of Fe2+ to Fe3+. The results obtained from Mössbauer spectroscopy (MS) were used to establish the chemical formulas of the synthesized spinels. Finally, the microstructure that was observed using scanning electron microscopy (SEM) showed a compact microstructure with an octahedral crystal habit.

Since the mechanism of the synthesis of magnetite from a stoichiometric mixture of hematite and iron is still under debate, systematic studies of the phase transformations in such powder mixture processed under field assisted sintering conditions, are presented. Phase contributions, grain sizes and stoichiometries of the sintered composites were determined using scanning electron microscopy, high energy X-ray diffraction and Mößbauer spectroscopy. It was shown that with an increasing sintering temperature an accelerated growth of magnetite can be observed, while the amount of hematite decreases. Additionally, intermediate wustite phase was observed with a maximum intensity where iron vanished from the samples. Therefore, it was concluded that the transition from hematite - iron mixture to magnetite actually takes place in two steps. In the first step, iron reduces hematite to magnetite and oxidizes itself to wustite. In the second step, wustite enables the nucleation of magnetite and with the help of hematite it transforms into nearly pure stoichiometric magnetite at higher sintering temperatures. In composites sintered from pure hematite under the same conditions only a minor transition to highly nonstoichiometric magnetite was observed emphasizing the above mentioned route of transformation.

MgO–ZrO2 ceramics were obtained by three different methods: conventional sintering, arc melting and field assisted sintering. The present study was undertaken in order to determine the influence of the different sintering techniques on the structural properties of MgO–ZrO2 ceramics. The phase compositions of the obtained samples consisted of MgO and ZrO2 cub. ss (doped by MgO). The amount of all phases in the final product and their average crystallite sizes are strongly influenced by the sintering method. The smallest crystallites were realized for ceramics consolidated by the field assisted sintering method (20.1±2.5nm for MgO and 27.0±2.7nm for ZrO2 cub. ss). About ten times larger crystallites resulted by conventional sintering. The average crystallite size in the material obtained by arc melting technique was around 116±20.4nm. It was observed that the microstructures of the samples prepared by arc melting and field assisted sintering are similar.

Magnetic iron oxide nanoparticles were prepared by salt-assisted solid-state chemical precipitation method with alternating fractions of the ferric iron content. The physical properties of the precipitated nanoparticles mainly consisting of magnetite were investigated by means of transmission electron microscopy, high energy X-ray diffraction, vibrating sample magnetometry and Mössbauer spectroscopy. With particle sizes ranging from 16.3nm to 2.1nm, a gradual transition from the blocked state to the superparamagnetic state was observed. The transition was described as a dependence of the ferric iron content used during the precipitation. Composition, mean particle size, coercivity, saturation polarisation, as well as hyperfine interaction parameters and their evolution were studied systematically over the whole series of iron oxide nanoparticles.

Vitrification is the most effective method for the immobilization of hazardous waste by incorporating toxic elements into a glass structure. Iron phosphate glasses are presently being considered as matrices for the storage of radioactive waste, even of those which cannot be vitrified using conventional borosilicate waste glass. In this study, a structural model of 60P2O5-40Fe2O3 glass is proposed. The model is based on the crystal structure of FePO4 which is composed of [FeO4][PO4] tetrahedral rings. The rings are optimized using the DFT method and the obtained theoretical FTIR and Raman spectra are being compared with their experimental counterparts. Moreover, the proposed model is in very good agreement with X-ray absorption fine structure spectroscopy (XANES/EXAFS) and Mössbauer spectroscopy measurements. According to the calculations the Fe(3+) is in tetrahedral and five-fold coordination. The maximal predicted load of waste constituents into the glass without rebuilding of the structure is 30 mol%. Below this content, waste constituents balance the charge of [FeO4](-) tetrahedra which leads to their strong bonding to the glass resulting in an increase of the chemical durability, transformation and melting temperatures and density.

A functional gradient material with eleven layers composed of a dental ceramics and titanium was successfully consolidated using field assisted sintering technique in a two-step sintering process. High energy X-ray diffraction studies on the gradient were performed at High Energy Material Science beamline at Desy in Hamburg. Phase composition, crystal unit edges and lattice mismatch along the gradient were determined applying Rietveld refinement procedure. Phase analysis revealed that the main crystalline phase present in the gradient is α-Ti. Crystallinity increases stepwisely along the gradient with a decreasing increment between every next layer, following rather the weight fraction of titanium. The crystal unit edge a of titanium remains approximately constant with a value of 2.9686(1)Å, while c is reduced with increasing amount of titanium. In the layer with pure titanium the crystal unit edge c is constant with a value of 4.7174(2)Å. The lattice mismatch leading to an internal stress was calculated over the whole gradient. It was found that the maximal internal stress in titanium embedded in the studied gradient is significantly smaller than its yield strength, which implies that the structure of titanium along the whole gradient is mechanically stable.

Electrical resistivity studies performed in a wide temperature range across the complete Fe/Co substituted Tb0.27Dy0.73(Fe1-xCox)(2) intermetallic series, with a borderline compound Tb0.27Dy0.73Fe2 known as Terfenol-D are presented. Parameters characterizing the dependence of resistivity on temperature, including the Debye temperature, are determined. Residual, phonon and magnetic contributions are separated from electrical resistivity. The magnetic contribution to electrical resistivity is applied to estimate Curie temperatures. Regions of weak and strong ferromagnetism of the transition metal sublattice are evidenced. The Curie temperature increases with x, approaches a maximum for x = 0.3 and reduces across the rest of the series. Some results of electronic band structure calculations using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method are also presented. A distribution function for the densities of 3d states is introduced and a formula to estimate the band splitting energy is proposed. The obtained 3d and 4s band splitting energies for iron, cobalt and average for transition metal are presented. The Curie temperature across the Tb0.27Dy0.73(Fe1-xCox)(2) system is described using a formula relating to both the FLAPW calculated magnetic moments and the statistical properties of the substituted transition metal sublattice. (C) 2013 Elsevier Ltd. All rights reserved.

Human body implants can be classified in general into two groups i.e. artificial bones for medical use and dental implants as artificial teeth for dental application. The implants in orthopedics are mostly used as structurally enforced artificial bone which is inserted inside the corpus. Dental implants are usually much smaller than medical implants and they are mostly applied to reconstruct the masticatory function if the tooth root is completely lost or extracted. Such dental implant is set in the jaw-bone from the outside and it has to replace bone tissue as well as the tooth itself [1]. Therefore, the function of a dental implant is quite different at different positions inside, outside or at the boundary of the bone. Current dental implants composed of only one material, sometimes covered with a coating layer, are essentially uniform in composition and structure. Thus, the concept of a functionally graded material (FGM) may be suitable for obtaining new dental implants.

Fe-57 Mossbauer effect spectra were collected at 4.2K for the Ho(Fe1-xCox)(2) C15 Laves phases. The hyperfine interaction parameters, i.e. isomer shift, the magnetic hyperfine field and the quadrupole interaction parameter, were determined for the individual Fe/Co nearest neighbourhoods of iron atoms and also as average values for the sample as bulk. As a result of Fe/Co substitution, Slater-Pauling-type dependences for magnetic hyperfine fields corresponding to both the local area and the sample as bulk were observed, and a linear correlation between the local magnetic hyperfine field and the average magnetic hyperfine field was observed. Magnetic moments of atoms were obtained from band structure calculations using the full-potential linearized augmented plane wave method. The magnetic hyperfine field obtained from the experiment correlates linearly (but separately for weak and strong ferromagnetic areas) with the magnetic moment calculated per transition metal atom.

The consequences of Fe/Ni substitution in Tb0.27Dy0.73(Fe1−xNix)2 intermetallics, with a starting compound Tb0.27Dy0.73Fe2 known as Terfenol – D, were studied. Ni substitution introduces a local area, at sub-nanoscale, with different Fe/Ni neighbourhoods of the 57Fe atoms. 57Fe Mössbauer effect measurements for the intermetallic system Tb0.27Dy0.73(Fe1−xNix)2 carried out at 4.2 K evidence an [100] easy axis of magnetization. Hyperfine interaction parameters – an isomer shift, a magnetic hyperfine field and a quadrupole interaction parameter – were determined from the fitting procedure of the spectra, both for the local neighbourhood area and, as averaged values, for the sample as bulk. As a result of Fe/Ni substitution, a Slater–Pauling type dependence for the average magnetic hyperfine field vs. Ni content is observed. Electronic band structure calculations using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method were performed. The relation between the experimentally determined magnetic hyperfine field and the weighted magnetic moment calculated per transition metal atom is discussed.

Synthesized, x-ray studied Ho(Fe1−xCox)2 compounds (x= 0–1) have a pure cubic Fd3m, C15, MgCu2-type crystal phase. The unit cell parameter decreases nonlinearly with the composition parameter x. Mössbauer effect spectra collected at 77 K for the Ho(Fe1−xCox)2 series were composed of a number of locally originated subspectra due to random Fe/Co nearest neighbourhoods. Hyperfine interaction parameters, i.e. the isomer shift, the magnetic hyperfine field and the quadrupole interaction parameter, were determined from the fitting procedure of the spectra for the individual nearest neighbourhoods and also as average values for the sample as bulk. As a result of Fe/Co substitution, Slater–Pauling-type dependences for magnetic hyperfine fields corresponding to both the local area and the sample as bulk were observed. A correlation between the local magnetic hyperfine fields and the average magnetic hyperfine fields was noticed, and this was related to weak and strong ferromagnetism of the transition metal sublattice. The obtained magnetic hyperfine fields were compared to analogous data known for compounds with other rare earths. A numerical formula for describing the magnetic hyperfine field as a function of the composition parameter x and rare earth spin S was proposed.

Synthesis of Ho(Fe1-xCox)(2) intermetallic compounds, studies of their crystal structure and Fe-57 Mossbauer effect analysis were carried out at 295 K. X-ray measurements evidence a pure cubic Fd3m, C15, MgCu2-type Laves phase. The unit cell parameter decreases non-linearly with composition parameter x. Mossbauer effect spectra for the Ho(Fe1-xCox)(2) series were composed of a number of locally originated subspectra due to random Fe/Co nearest neighbourhoods. Hyperfine interaction parameters, i.e. isomer shift, the magnetic hyperfine field and a quadrupole interaction parameter were determined from the fitting procedure of the spectra, for both the individual nearest neighbourhoods, and for the sample as bulk. As a consequence of Fe/Co substitution a Slater-Pauling type curve for the average magnetic hyperfine field vs. x is observed. The correlation between the local magnetic hyperfine fields and the average magnetic hyperfine fields is related to weak and strong ferromagnetism of the transition metal sublattice.