The crystallographic orientation relationship between Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> in the composite material Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al–Mg–Si alloy

The formation mechanism of spinels on Al₂O₃ particles in the Al₂O₃/Al–1.0 mass% Mg₂Si alloy composite material has been investigated by transmission electron microscopy (TEM) in order to determine the crystallographic orientation relationship. A thin sample of the Al₂O₃/Al–Mg–Si alloy composite material was obtained by the FIB method, and the orientation relationship between Al₂O₃ and MgAl₂O₄, which was formed on the surface of Al₂O₃ particles, was discovered by the TEM technique as follows:

Reaction diffusion in the Nb-Ge system

Reaction diffusion in the Nb-Ge system was studied in the temperature range 1243 to 1723 K for diffusion couples of (pure solid Nb)-(pure liquid Ge) and (pure solid Nb)-(Ge-37.5wt % Nb liquid alloy). Growth of the NbGe₂, Nb₃Ge₂, Nb₅Ge₃ and Nb₃Ge layers was observed, and the growth rates of all except the Nb₃Ge layer were found to conform to the parabolic law. Growth of the Nb₃Ge layer was observed only along the grain boundaries in the Nb₅Ge₃ layer. Interdiffusion coefficients \(\tilde D\) in the NbGe₂, Nb₃Ge₂ and Nb₅Ge₃ phases were determined by Heumann's method, and the temperature dependence of these was expressed by the Arrhenius equations as follows: $$\tilde D_{{\text{NbGe}}_{\text{2}} } = (6.40_{ - 1.66}^{ + 2.25} \times 10^{ - 6} exp [ - (161 \pm 4) kJ mol^{ - 1} {\text{/RT] m}}^{{\text{2 }}} \sec ^{ - 1} $$ $$\tilde D_{{\text{Nb}}_{\text{3}} {\text{Ge}}_{\text{2}} } = (2.27_{ - 0.60}^{ + 0.82} \times 10^{ - 4} exp [ - (282 \pm 4) kJ mol^{ - 1} {\text{/RT] m}}^{{\text{2 }}} \sec ^{ - 1} $$ and $$\tilde D_{{\text{Nb}}_{\text{5}} {\text{Ge}}_{\text{3}} } = (6.28_{ - 1.93}^{ + 2.78} \times 10^{ - 5} exp [ - (238 \pm 5) kJ mol^{ - 1} {\text{/RT] m}}^{{\text{2 }}} \sec ^{ - 1} $$ In addition to the binary Nb-Ge system, the reaction diffusion of (pure solid Nb)-(Cu-13 wt % Ge liquid alloy) couples was also studied. In this case, only growth of the Nb₅Ge₃ layer containing negligible copper content was observed.     

Insights into the structural,electronic, and magnetic properties of Fe2−x Ti x O3/Fe2O3 thin films with x = 0.44 grown on Al2O3 (0001)

The interface between hematite (α-Fe ₂ ^III O₃) and ilmenite (Fe^IITiO₃), a weak ferrimagnet and an antiferromagnet, respectively, has been suggested to be strongly ferrimagnetic due to the formation of a mixed valence layer of Fe²⁺/Fe³⁺ (1:1 ratio) caused by compensation of charge mismatch at the chemically abrupt boundary. Here, we report for the first time direct experimental evidence for a chemically distinct layer emerging at heterointerfaces in the hematite—Ti-doped-hematite system. Using molecular beam epitaxy, we have grown thin films (~25 nm thickness) of α-Fe₂O₃ on α-Al₂O₃ (0001) substrates, which were capped with a ~25 nm thick Fe_2?x Ti _x O₃ layer (x = 0.44). An additional 3 nm cap of α-Fe₂O₃ was deposited on top. The films were structurally characterized in situ with surface X-ray diffraction, which showed a partial low index orientation relationship between film and substrate in terms of the [0001] axis and revealed two predominant domains with \( (0001) _{{{\text{Fe}}_{2} {\text{O}}_{3} }} \;||\;(0001) _{{{\text{Al}}_{2} {\text{O}}_{3} }}, \) one with \( [10\bar{1}0]_{{{\text{Fe}}_{2} {\text{O}}_{3} }} \;||\;[10\bar{1}0]_{{{\text{Al}}_{2} {\text{O}}_{3} }}, \) and a twin domain with \( [01\bar{1}0]_{{{\text{Fe}}_{2} {\text{O}}_{3} }} \;||\;\;[10\bar{1}0]_{{{\text{Al}}_{2} {\text{O}}_{3} }}. \) Electron energy loss spectroscopy profiles across the Fe_2?x Ti _x O₃/Fe₂O₃ interface show that Fe²⁺/Fe³⁺ ratios peak right at the interface. This strongly suggests the formation of a chemically distinct interface layer, which might also be magnetically distinct as indicated by the observed magnetic enhancement in the Fe_2?x Ti _x O₃/α-Fe₂O₃/Al₂O₃ system compared to the pure α-Fe₂O₃/Al₂O₃ system.     

Novel method for fabrication of NiO sensor for NO2 monitoring

Nickel oxide (NiO) sensor films were prepared on glass substrate by a sol–gel spin coating technique. These films were characterized for their structural and morphological properties by means of X-ray diffraction, field emission scanning microscopy and atomic force microscopy. The NiO films are oriented along (200) plane with the cubic crystal structure. These films were utilized in nitrogen dioxide gas (NO₂) sensor. The dependence of the NO₂ response on operating temperature, NO₂ concentration was investigated. The NiO film showed selectivity for NO₂ over Cl₂ compared to H₂S $ \left( {{\text{S}}_{{{\text{NO}}_{ 2} }} /{\text{S}}_{{{\text{Cl}}_{ 2} }} = 3 7. 5,{\text{ S}}_{{{\text{NO}}_{ 2} }} /{\text{S}}_{{{\text{H}}_{ 2} {\text{S}}}} = 3. 4} \right) $ . The maximum NO₂ response of 23.3 % with 85 % stability at gas concentration of 200 ppm at 200 °C was achieved. The response time of 20 s and recovery time of 498 s was also recorded with same operating parameters.     

Mass transfer through a single grain boundary in alumina bicrystals under oxygen potential gradients

The mass-transfer behavior through grain boundaries (GBs) in alumina was systematically investigated using four types of alumina bicrystals. The alumina bicrystal wafers were exposed to the constant oxygen potential gradient $ \left( {\Updelta P_{{{\text{O}}_{ 2} }} } \right) $ generated by the combination of two different oxygen partial pressures $ P_{{{\text{O}}_{ 2} }} \left( {\text{II}} \right) $ and $ P_{{{\text{O}}_{ 2} }} \left( {\text{I}} \right) $ of 10⁵ and 1?Pa, respectively, at 1923?K. Ridges were formed along the GBs on the surface subjected to $ P_{{{\text{O}}_{ 2} }} \left( {\text{II}} \right) $ , and deep GB ditches were developed on the $ P_{{{\text{O}}_{ 2} }} \left( {\text{I}} \right) $ surface mainly during the migration of aluminum thorough GBs from the $ P_{{{\text{O}}_{ 2} }} \left( {\text{I}} \right) $ surface to $ P_{{{\text{O}}_{ 2} }} \left( {\text{II}} \right) $ surface. The surface morphology changes in the vicinity of the GBs were observed by atomic force microscopy. It was found that the surface morphology changes indicative of the aluminum GB diffusion were strongly dependent on the GB characteristics. The GB diffusion coefficients of aluminum estimated from the volume of the GB ridges showed a clear correlation to the local bonding environments of GB cores estimated from theoretical calculations reported previously.     

Synthesis of ZnO single crystals by the flux method

Zinc oxide (ZnO) single crystals have been grown at temperatures ranging from 450–900 °C and for 1–12 h, using hydrous KOH and NaOH melts as fluxes. For a KOH flux, brown ZnO single crystals with diameter 0.5 mm × 7.5 mm were grown under conditions of 500 °C for 20 h and white crystals of diameter 0.5 mm × 7 mm were grown at 800 °C for 20 h, using a small crucible (average 50 ml). When a large crucible (average 400 ml) was used, ZnO single crystals with diameter 0.5 mm × 8 mm were formed at 900 °C for 30 h. When using a KOH + NaOH (1∶1) flux, light-brown and long crystals with diameter 1.0 mm × 18 mm could be grown. The grown ZnO single crystals were bounded with only both p- and m-faces. It seems that crystal qualities were good under conditions of 900 °C for 30 h. The following mechanisms of dissociation and formation of ZnO single crystal from KOH (or NaOH) + ZnO melt seemed to occur $$KOH(or{\text{ NaOH}}){\text{ }} \to {\rm K}^ + {\text{ (or Na}}^{\text{ + }} {\text{) + OH}}^ - $$ $$ZnO{\text{ + 2 OH}}^ - \to {\text{ ZnO}}_{\text{2}}^{{\text{2}} - } {\text{ + H}}_{\text{2}} {\text{O,}}$$ $${\text{ZnO}}_{\text{2}}^{{\text{2}} - } {\text{ }} \to {\text{ ZnO + O}}^{{\text{2}} - } .$$      

HRTEM study of [001] low-angle tilt grain boundaries in fiber-textured BaTiO3 thin films

Low-angle tilt grain boundaries in [001] fiber-textured BaTiO₃ thin films were investigated by high-resolution transmission electron microscopy. Extensive observation revealed a very high density of low-angle tilt grain boundaries in the film. The low-angle tilt grain boundaries can be described as periodical arrays of dislocations on {100} and {110} boundary planes. The boundaries with (100) plane on {100} planes are composed of perfect dislocations with Burgers vectors b = a < 100 > (a = lattice constant of BaTiO₃: 0.3992 nm), while the boundaries with (110) plane on {110} planes are composed of the dissociated dislocations with Burgers vectors a/2 < 110 >. It was thus found that the difference in the boundary plane leads to different dislocation structures along the low-angle grain boundaries.     

Fabrication and characterization of iron and fluorine co-doped BST thin films for microwave applications

The effects of fluorine co-doping by means of a post-thermal annealing process of iron-doped BST thin films in a fluorine-containing atmosphere have been investigated. XPS and ToF-SIMS sputter depth profiling verified a homogeneous fluorine distribution in the thin films. By employing EPR, it was shown that singly charged ( $ {\text{Fe}}_{\text{Ti}}^{\prime } $ – $ {\text{V}}_{\text{O}}^{ \cdot \cdot } $ )^· defect complexes, as well as ‘isolated’ $ {\text{Fe}}_{\text{Ti}}^{\prime } $ centres with a distribution of $ {\text{F}}_{\text{O}}^{ \cdot } $ sites in remote coordination spheres exist in the fluorinated films. Tunability enhancement due to fluorine co-doping as well as a Q-factor enhancement due to iron doping is demonstrated.     

Thermoelectric properties of porous n-type {\text{Fe}}_{{\text{0}}{\text{.94}}} {\text{Co}}_{{\text{0}}{\text{.06}}} {\text{Si}}_{\text{2}} compounds prepared by pressureless sintering

The effects of bulk porosity on the thermoelectric properties of porous n-type ${\text{Fe}}_{{\text{0}}{\text{.94}}} {\text{Co}}_{{\text{0}}{\text{.06}}} {\text{Si}}_{\text{2}} $ compounds prepared by pressureless sintering were examined. A small amount of metallic phase ?-FeSi remained after annealing at 800 °C for 100 h. As the sintering temperature increased from 1150 to 1175 °C, the phase transition to β-FeSi₂ during annealing occurred more rapidly. The porous specimen, sintered at 1150 °C for 2 h with coarse powders (<45 μm) and then annealed at 800 °C for 100 h, showed the highest Seebeck coefficient of $ - 363_{\mu } {VK}^{ - {1}} $ at 400 °C and the highest power factor of ${\text{1}}{\text{.57}} \times 10^{ - 3} {\text{Wm}}^{ - 1} {\text{K}}^{ - 2} $ at 400 °C.     

Surface and grain-boundary energies of cubic zirconia

Using the multiphase equilibration technique for the measurement of contact angles, the surface and grain-boundary energies of polycrystalline cubic ZrO₂ in the temperature range of 1173 to 1523 K were determined. The temperature coefficients of the linear temperature function obtained, are expressed as $$\frac{{{\text{d}}\gamma }}{{{\text{d}}T}}({\text{ZrO}}_{\text{2}} ){\text{ }} = {\text{ }} - 0.431{\text{ }} \times {\text{ }}10^{ - 3} {\text{ }} \pm {\text{ }}0.004{\text{ }} \times {\text{ }}10^{ - 3} {\text{ Jm}}^{ - {\text{2}}} {\text{ K}}^{ - {\text{1}}} $$ and $$\frac{{{\text{d}}\gamma }}{{{\text{d}}T}}({\text{ZrO}}_{\text{2}} - {\text{ZrO}}_{\text{2}} ){\text{ }} = {\text{ }} - 0.392{\text{ }} \times {\text{ }}10^{ - 3} {\text{ }} \pm {\text{ }}0.126{\text{ }} \times {\text{ }}10^{ - 3} {\text{ Jm}}^{ - {\text{2}}} {\text{ K}}^{ - {\text{1}}} $$ respectively. The surface fracture energy obtained with a Vickers microhardness indenter at room temperature is found to be γ _F=3.1 J m^?2.     

Determination of standard Gibbs energies of formation of ternary oxides in the system Co-Sb-O by solid electrolyte emf method

An isothermal section of the phase diagram of the system Co-Sb-O at 873 K was established by isothermal equilibration and XRD analyses of quenched samples. The following galvanic cells were designed to measure the Gibbs energies of formation of the three ternary oxides namely CoSb₂O₄, Co₇Sb₂O₁₂ and CoSb₂O₆ present in the system.

Effect of boundary plane on the atomic structure of [0001] Σ 7 tilt grain boundaries in ZnO

The atomic structure of [0001] Σ 7 tilt grain boundaries with { }‖ { }, { }‖ { }, and { }‖ { } boundary planes in ZnO was investigated through high-resolution transmission electron microscopy observation of fiber-textured thin films and atomistic calculations. These boundaries were found to comprise three kinds of common structural units that are characterized by fourfold- to eightfold-coordinated channels along the [0001] direction in contrast to sixfold-coordinated channels in wurtzite structure. The boundary structural units are very similar to the multiple core structures of edge dislocations with Burgers vectors of 1/3 < > . Transformation between two of the three configurations can easily occur through an atom flipping corresponding to dislocation glide. Depending on the orientation of boundary planes with respect to the Burgers vectors, the dislocation-like units exhibit straight or zigzag arrangements with periodicities corresponding to the Σ 7 misorientation.     

Electrical conductivity of polycrystalline tin dioxide and its solid solution with ZnO

Electrical conductivity (σ) of “pure” and ZnO doped SnO₂ has been measured at different temperatures and oxygen partial pressures ( \(p_{{\text{O}}_{\text{2}} } \) )- From the variation of electrical conductivity of these materials three partial pressure ranges have been identifieD. In the high partial pressure rangeσ increases with decreasing \(p_{{\text{O}}_{\text{2}} } \) followed by a \(p_{{\text{O}}_{\text{2}} } \) independent region at lower \(p_{{\text{O}}_{\text{2}} } \) ´s and finally increases once again with a further decrease of \(p_{{\text{O}}_{\text{2}} } \) . These variations have been explained on the basis of an anti-Frenkel type defect structure and an interstitial solid solution of ZnO in SnO₂. The activation energy for the conduction process has been estimated and the values are found to differ in two different temperature ranges. In the low temperature range the conductivity is attributed mainly to the chemisorption of oxygen on the surface of the specimen.     

Effects of Bi doping on dielectric and ferroelectric properties of PLBZT ferroelectric thin films synthesized by sol–gel processing

[Pb _0·95(La_1???y Bi _y ) _0·05][Zr_0·53Ti_0·47]O₃ (PLBZT) ferroelectric thin films have been synthesized on indium tin oxide (ITO)-coated glass by sol–gel processing. PLBZT thin films were annealed at a relatively low temperature of 550 °C in oxygen ambient. Effects of Bi doping on structure, dielectric and ferroelectric properties of PLBZT were investigated. Bi doping is useful in crystallization of PLBZT films and promoting grain growth. When the Bi-doping content ${\mathit{y}}$ is not more than 0·4, an obvious improvement in dielectric properties and leakage current of PLBZT was confirmed. However, when the Bi-doping content is more than 0·6, the pyrochlore phase appears and the remnant polarization P _r of PLBZT thin films is smaller than that of $\left({Pb}_{{1-x}} {\bf La}_{x}\right)\!\!\left({Zr}_{{1-y}} {Ti}_{y}\right){O}_{3}$ (PLZT) thin films without Bi doping. PLBZT thin films with excessive Bi-doping content are easier to fatigue than PLZT thin films.     

Correlation of luminescent properties of ZnO and Eu doped ZnO nanorods

ZnO and ZnO:Eu nanorods were originally synthesized by concussion method. The nanorods present a wurtzite nanostructure with dispersive distribution morphology. The average diameter and length of the nanorods are about 80 nm and 2 μm, respectively. The best concussion time, concussion frequency, the function of HMT and the growth mechanism are presented in this paper. This method is simple, economical, and environmentally mild. We believe other kinds of ZnO nanostructures could be obtained by this method when appropriate agents are added. However, because of the different chemical properties between trivalent RE ions and the cations of ZnO, it is rather difficult to incorporate RE ions into the lattice of semiconductors effectively via a wet chemical method. Based on our experiments, the sample of $ {\text{ZnO}}:{\text{Eu}}^{3 + }_{1\% } $ is single-phase and its PL signal is stronger than other single-phase $ {\text{ZnO}}:{\text{Eu}}^{3 + }_{X} $ samples. So 1% content of Eu³⁺ was chosen as the best doping concentration.     

Major effects on varistor properties and impulse aging behavior of Zn–V–Mn–Co–Dy ceramics with small sintering changes

The effect of sintering temperature on varistor properties and impulse aging behavior of ZnO–V₂O₅–MnO₂–CoO–Dy₂O₃ ceramics was systematically investigated. As the sintering temperature increased, the average grain size increased from 5.8 to 10.8 μm, whereas the sintered density decreased from 5.56 to 5.47 g/cm³. The breakdown field and the nonlinear coefficient increased from 1,812 to 3,379 V/cm and from 11 to 36, respectively, with an increase in the sintering temperature up to 925 °C. The varistor ceramics sintered at 950 °C exhibited the best clamp characteristics for the impulse-current of 1–50 A, with the clamp voltage ratio of K = 1.63–2.31. The varistor ceramics sintered at 925 °C exhibited the strongest stability against an impulse-current, with $ \% \,\Updelta {\text{E}}_{{ 1 {\text{ mA}}/{\text{cm}}^{2} }} = - 8. 1 \,\% ,\;\%\, \Updelta \alpha = - 4 4. 4\, \% ,{\text{ and}}\;\%\, \Updelta {\text{J}}_{\text{L}} = 3 8. 9\, \% $ % Δ E 1 mA / cm 2 = ? 8.1 % , % Δ α = ? 4 4.4 % , and % Δ J L = 3 8.9 % after applying the multi-impulse-current of 400 A.     

High energy impact techniques application for surface grain refinement in AZ91D magnesium alloy

A nanostructured surface layer was fabricated on magnesium alloy AZ91D by using the high-energy impact technique (HEIT). With the help of transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM), the microstructure features of the surface layer were systematically observed and characterized in different stages of microstructure evolution. The result revealed the mechanism of grain refinement and strain accommodation. The process of grain refinement, accompanied by an increase in strain in the surface layer, resulted from several processes. The onset of deformation twinning and the intersection with twins system are one of them. The operation of basal slip and pyramidal slip led to the formation of dislocation cells and low-angle dislocation boundaries. The successive subdivision of grains to a finer scale resulted in the formation of highly disoriented nanocrystalline grains. The mechanism of grain refinement was interpreted in terms of the structural subdivision of grains together with dynamic recrystallization. The minimum size of such refined grains was about 40 nm.     

Dissociation reaction of the 1/3$$ \left\langle {\bar{1}101} \right\rangle $$ edge dislocation in α-Al2O3

It has been reported that dislocations with 1/3\( \left\langle {\bar{1}101} \right\rangle \) edge component of the Burgers vector are formed in {1\( \bar{1} \)04}/\( \left\langle {11\bar{2}0} \right\rangle \) low-angle grain boundaries of alumina (α-Al₂O₃). These dislocations dissociate into two partial dislocations with a stacking fault on the (0001) plane (Tochigi et al. in J Mater Sci 46:4428–4433, 2011). However, the dissociation reaction of these dislocations has not been determined so far. In this study, the structures of the dissociated dislocations and the (0001) stacking fault were investigated by transmission electron microscopy and theoretical calculations. It was revealed that the dissociated dislocations were generated from the 1/3\( \left\langle {\bar{1}101} \right\rangle \) perfect edge dislocation by the reaction of 1/3\( \left\langle {\bar{1}101} \right\rangle \) → 1/18\( \left\langle {\bar{4}223} \right\rangle \) + 1/18\( \left\langle {\bar{2}4\bar{2}3} \right\rangle \). Furthermore, electron energy loss spectroscopy analysis was performed to examine the atomic/electronic structure of the (0001) stacking fault. In the observed spectra, a chemical shift and intensity decrease were found at the oxygen K-edge. Theoretical spectrum analysis using first-principles calculations revealed that the characteristic features of the spectra are originated from the local atomic configurations of the (0001) stacking fault.     

Stability and direct conversion of mineral barite crystals in carbonated hydrothermal fluids

The pseudomorphic replacement of mineral barite (BaSO₄) crystals into barium carbonate was investigated in the present work by using carbonated alkaline hydrothermal fluids. Hydrothermal treatments were carried out over the temperature range from 150 up to 250 °C for intervals between 1 and 192 h, with different filling ratios (40–70%), and molar ratios of 1, 5, and 10. The reaction products were characterized by XRD and SEM techniques. The chemical reactivity of mineral barite crystals was markedly limited at temperatures below 200 °C, and only a tiny BaCO₃ layer on the surface of the original BaSO₄ crystal was formed on the crystal treated for 192 h. The rate of the pseudomorphic conversion of BaSO₄ into BaCO₃, was accelerated by increasing the reaction temperature and the molar ratio . Powder X-ray diffraction results showed that under hydrothermal conditions the replacement of ions by ions, in barite crystals was completed at 250 °C with a molar ratio = 10 for an interval of 192 h, resulting in the Witherite structure. The morphology of the completely converted BaCO₃ at 250 °C in a Na₂CO₃ solution for 192 h, showed that the conversion proceed without severe changes of the original shape and dimension of the original crystal, similar to that observed in mineral pseudomorphic replacement process.