Specific features of solid HDDR in alloys based on SmCo<Subscript>5</Subscript> in low-pressure hydrogen

The methods of differential thermal analysis and X-ray phase-diffraction analysis are used for the investigation of the interaction of an alloy based on the SmCo₅ compound with hydrogen. The alloy is held in hydrogen for 2 and 5h under pressures of 200, 300, 400, and 500 kPa in the temperature range 473–1223°K. The interaction of the alloy with hydrogen at 973°K under the pressures {ie602-01}, 300, and 400 kPa leads to the transformation of the SmCo₃ impurity phase into an unidentified phase or unidentified phases. As the hydrogen pressure rises to {ie602-02}, we observe the formation of a mixture of SmCo₅ and SmH_x and the appearance of the traces of γ-Sm₂Co₁₇. At 1223°K, for all levels of hydrogen pressure in the process of interaction, the compositions of the products of hydrogen-induced phase transformations are identical, namely, SmCo₅, SmH_x, and Sm₂Co₁₇. Moreover, for {ie602-03}, 400, and 500 kPa, we detect the traces of Co. It is shown that the amounts of samarium hydride and the Sm₂Co₁₇ phase increase with the pressure of hydrogen. It is shown that, as the time of holding under a pressure {ie602-04} increases to 5h, the degree of disproportionation of SmCo₅ increases. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 4, pp. 121–126, July–August, 2008.     

Hydrogen-induced phase transformations in Sm-Co alloy under the action of ultrasound

By the method of X-ray phase diffraction analysis, we study specific features of the action of ultrasound with a frequency of 44 kHz on the interaction of an alloy based on SmCo₅ (SmCo₃ is an impurity) with hydrogen at pressures of 200–500 kPa and temperatures lower than 1223°K under the conditions of hydrogenation and disproportionation. It is shown that at 473 and 773°K, the impurity phase transforms into unidentified products. At 913°K, the alloy partially disproportionates into SmH_x and Co. The degree of disproportionation increases as a result of holding at 913°K. Above 1173°K, we identify SmCo₅, SmH_x, and Sm₂Co₁₇. The ultrasonic treatment accelerates the hydrogen-induced phase transformations. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 71–75, September–October, 2007.     

Microstructure and H<Subscript>2</Subscript>S gas sensing properties of nanocrystalline perovskite-type La<Subscript>0.6</Subscript>Co<Subscript>0.4</Subscript>Mn<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>O<Subscript>3</Subscript>

Nanocrystalline La_1−x Co _x Mn_1−y Ni _y O₃ (x = 0.2 and 0.4; y = 0.1, 0.3, and 0.5) thick films sensors prepared by sol–gel method were studied for their H₂S gas sensitivity. The structural and morphological properties have been carried out by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Average particle size estimated from XRD and TEM analyses was observed to be 30–35 nm. The gas response characteristics were found to depend on the dopants concentration and operating temperature. The maximum H₂S gas response of pure LaMnO₃ was found to be at 300 °C. In order to improve the gas response, material doped with transition metals Co and Ni on A- and B-site, respectively. The La_0.6Co_0.4Mn_0.5Ni_0.5O₃ shows high response towards H₂S gas at an operating temperature 250 °C. The Pd-doped La_0.6Co_0.4Mn_0.5Ni_0.5O₃ sensor was found to be highly sensitive to H₂S at an operating temperature 200 °C. The gas response, selectivity, response time and recovery time were studied and discussed.     

Occurrence and stability of ferromagnetism in chemically synthesized cobalt doped TiO<Subscript>2</Subscript>

We report the development of ferromagnetism in ∼30 nm sized well-characterized Ti_1−x Co _x O₂ powders with x = 0.00015–0.006 and its absence for x > 0.006. In addition, these studies show the effect of Co doping on the structural stability and anatase to rutile phase transformation. X-ray diffraction data of samples synthesized by a wet chemical method and annealed at 450 °C indicate a limited solubility of ∼1.2% for Co in the anatase TiO₂ matrix, and with further increase, the CoTiO₃ phase is formed along with increased presence of rutile TiO₂. The bandgap (∼3.23 eV) of the anatase TiO₂ remained almost unchanged for x < 0.006, but decreased rapidly for x ≥ 0.006 approaching 2.8 eV for x = 0.03. The magnetic data from Ti_1−x Co _x O₂ samples with x = 0.006 showed a coercivity H _c ∼ 150 Oe and a weak magnetic moment of 0.2 μ_B/ion at 300 K. The ferromagnetism of Ti_0.994Co_0.006O₂ with open hysteresis loops continue up to a high superparamagnetic blocking temperature T _B ∼ 675 K, above which a superparamagnetic behavior was observed. Systematic changes in the structural, magnetic and optical properties suggest that Co doping is an excellent method to tailor the physical properties of TiO₂ nanoparticles.     

The synthesis and the magnetic properties of Sm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>BiY<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>5</Subscript>O<Subscript>12 </Subscript>nanoparticles

Sm _x BiY_2–x Fe₅O₁₂ (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8) nanocrystals were fabricated by sol–gel method. Samples were characterized by powder X-ray diffraction (XRD), thermal gravity analysis (TGA) and differential thermal analysis (DTA), transmission electron microscopy (TEM), vibrating sample magnetometer(VSM). The samples were calcined at 850 °C and 1000 °C and the average size of the particles were determined by Scherrer’s formula . In this paper, we discussed the effect of Sm³⁺ substitution for Y³⁺ on magnetic properties of BiY₂Fe₅O₁₂. The magnetic properties of Sm _x BiY_2−x Fe₅O₁₂ are decreased with increasing content of Sm ion.     

The influence of alloying Fe<Subscript>59</Subscript>Pt<Subscript>41</Subscript> thin films with Co on their magnetic and microstructural properties

This study investigates how the addition of Co to a Fe₅₉Pt₄₁ alloy with compositions in the range of Fe₅₉Pt₄₁–Co₅₉Pt₄₁ affects the crystallographic ordering temperatures and magnetic properties of sputter-deposited films. Introducing Co into the (Fe_1−x Co _x )₅₉Pt₄₁ film affects the activation energy of atomic migration and grain growth, thus leading to a higher annealing temperature of the L1₀ phase formation. At a Co concentration of x = 0.2, the saturation magnetization was maximum, at 1,480 emu/cm³, and the (Fe_0.8Co_0.2)₅₉Pt₄₁ film exhibited a coercivity of about 4 kOe.     

Crystal structure and methane oxidation on perovskite-type (La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Nd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)CoO<Subscript>3</Subscript> synthesized using citric acid

Perovskite-type (La_1−x Nd _x )CoO₃ was synthesized using citric acid at 700 °C. The Rietveld method indicated that the crystal structure changed from a rhombohedral to an orthorhombic system at x = 0.4. The Co–O distance of the rhombohedral structure connected continuously with the average Co–O(2) distance of the orthorhombic structure, and the Co–O–Co angle of the rhombohedral structure and the Co–O(2)–Co angle of the orthorhombic structure were continuous. The average particle size of the samples was approximately 55 nm. CH₄ oxidation started above 300 °C, and the temperature corresponding to the 50% conversion (T _1/2) of CH₄ increased linearly with increases in x. It is considered that the amount of adsorbed oxygen decreased in response to the steric hindrance, and that T _1/2 increased as a result.     

Characterisation of Sm–Co–Sn alloys

Cast SmCo_5?xSn_x (x = 0.00, 0.01, 0.06 and 0.12) alloys were prepared by arc melting with subsequent thermal homogenisation. Microstructural and x-ray diffraction studies revealed that the alloys were constituted of three phases i.e. SmCo₅, Sm₂Co₇ and Sm₂Co₁₇. The addition of Sn caused grain refinement of the alloys. It was found that the Sn addition promoted nucleation of Sm₂Co₁₇, segregation of solute atoms and increase in unit cell volume; consequently, significant augmentation in remanence to maximum magnetization ratios was achieved.     

Structure of an alloy based on SmCo5 after disproportionation-recombination

By using the X-ray phase diffraction, metallographic, and micro-X-ray spectral analyses, we study the procedure of solid hydrogenation, disproportionation, desorption, and recombination in KS37 alloy formed by the SmCo₅ and SmCo₃ phases for ≈ 4 MPa at 1158°K. The alloy disproportionates in hydrogen into a mixture of samarium hydride and cobalt with grain sizes ≤ 1 μm. The process of recombination ends by the restoration of the original phases accompanied by the formation of a fine-grained structure of the SmCo₃ phase. As a result, the amount of this phase decreases. The procedure of holding of the alloy for 55 min in the course of recombination leads to the formation of a structure with elongated grains. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 65–68, September–October, 2006.     

Influence of Sm substitution on the phase,microstructure and microwave dielectric properties of SrLa<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>17</Subscript>

New dielectric ceramics in the SrLa_4−xSm_xTi₅O₁₇ (0 ≤ x ≤ 4) composition series were prepared through a solid state mixed oxide route to investigate the effect of Sm⁺³ substitution for La⁺³ on the phase, microstructure and microwave dielectric properties. At x = 0–3, all the compositions formed single phase ceramics within the detection limit of in-house X-ray diffraction when sintered in the temperature range 1500–1580 °C. At x = 4, a mixture of Sm₂Ti₂O₇ and SrTiO₃ formed. The maximum Sm⁺³-containing single phase ceramics, SrLaSm₃Ti₅O₁₇, exhibited relative permittivity (ε_r) = 42.6, temperature coefficient of resonant frequency (τ _f ) = −96 ppm/^oC and quality factor (Q _u f _o ) = 7332 GHz. An analysis of results presented here indicates that SrLa_4−xSm_xTi₅O₁₇ ceramics, exhibiting τ _f  ~ 0 and ε_r ~ 53 could be achieved at x ~ 1.4 but at the cost of decrease in Q _u f _o .     

Room-Temperature Photomagnetic Effect of Fe<Subscript>3</Subscript>Ga<Subscript>4</Subscript> Grown on GaAs Substrates

Ga–As–Fe composite films prepared by molecular beam epitaxy at 600°C on GaAs(100) substrates with the stacking sequence of [100-nm GaAs/50-nm Fe₃Ga_{2− x} As _x /100-nm GaAs] exhibit the distinct photo-enhanced magnetization at room temperature. Transmission electron microscopy reveals the formation of metamagnetic Fe₃Ga₄ grains on the sample surface. Illumination power dependence of the enhanced magnetization has been carefully compared with the antiferromagnetic-type magnetization–temperature (M–T) curve (Neel temperature of T _N = 340–390 K), from which we have discussed the existence of photon-mode photo-enhanced magnetization of some sort in addition with the enhancement due to the light-induced heating.     

Phase component and conductivities of Co-doped BaTiO<Subscript>3</Subscript> thermistors

BaTi_1−x Co _x O_3−δ (0.01 ≤ x ≤ 0.4) ceramics were prepared by a wet chemical process polymerized with polyvinyl alcohol. The phases and related electrical properties of the ceramics were investigated. The phase component of the ceramics changes from a tetragonal phase to a hexagonal one with the Co concentration increase. A pure hexagonal phase formed in the ceramic with x = 0.2. The measurement of the temperature dependence of resistances revealed that the ceramic resistivities increase with temperature rising at the temperatures (T) lower than half of the related Debye temperature (Θ_D), and the ceramics show a negative temperature coefficient (NTC) effect at T > Θ_D/2. The material constants B _50/120 of the BaTi_1−x Co _x O_3−δ NTC thermistors were calculated to be 3,187, 2,968 and 2,648 K for x = 0.2, 0.3 and 0.4, respectively. Narrow-band conduction and non-adiabatic hopping models are proposed for the conduction mechanisms at T < Θ_D/2 and T > Θ_D/2, respectively.     

Dielectric and ferromagnetic properties of BaTiO<Subscript>3</Subscript>/Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Cu<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

xBaTiO₃ + (1 − x)Ni_0.93Co_0.02Cu_0.05Fe₂O₄ (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to 15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation magnetization (M _s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric materials.     

Effects of addition of BiFeO<Subscript>3</Subscript> on phase transition and dielectric properties of BaTiO<Subscript>3</Subscript> ceramics

Samples of xBiFeO₃–(1 − x)BaTiO₃ (x = 0, 0.02, 0.04, 0.06, 0.07 and 0.08) were synthesized by solid state reaction technique and sintered in air in the temperature range 1,220–1,280 °C for 4 h. X-ray diffraction data showed that 2–8 mol% BiFeO₃ can dissolve into the lattice of BaTiO₃ and form single perovskite phase. The crystal structure changes from tetragonal to cubic phase at room temperature when 8 mol% of BiFeO₃ was added into BaTiO₃. Scanning electron microscope images indicated that the ceramics have compact and uniform microstructures, and the grain size of the ceramics decreases with the increase of BiFeO₃ content. Dielectric constants were measured as functions of temperatures (25–200 °C). With rising addition of BiFeO₃, the Curie temperature decreases. For the sample with x = 0.08, the phase transition occurred below room temperature. The boundary between tetragonal and cubic phase of the BiFeO₃–BaTiO₃ system at room temperature locates at a composition between 7 and 8 mol% of BiFeO₃. The diffusivity parameter γ for compositions x = 0.02 and x = 0.07 is 1.21 and 1.29, respectively. The relaxor-like behaviour is enhanced by the BiFeO₃ addition.     

Polarization Effect in ESR of Co Doped CuGeO<Subscript>3</Subscript>

Electron spin resonance of a single crystal of CuGeO₃ doped with 2% of Co has been studied at f = 99 GHz in temperature range 1.8–50 K. Contributions to ESR absorption from Cu²⁺ chains and from Co²⁺ ions were derived. It is found that functions obtained for ESR integrated intensities: Curie-Weiss for Cu²⁺ (χCu ∼ C _Cu/(T + Θ), with Θ = 92 K) and Curie for Co²⁺ (χCo ∼ C _Co/T) are well consistent with temperature dependence of static magnetic susceptibility. Strong dependence of ESR absorption on polarization of oscillating magnetic field was discovered for Co²⁺ contribution. Polarization effect was studied for magnetic field applied along a, b and c directions. Values of g-factors of resonance lines are presented.     

Wetting of grain boundaries in Al by the solid Al<Subscript>3</Subscript>Mg<Subscript>2</Subscript> phase

The microstructure of binary Al_100−x –Mg _x (x = 10, 15, 18 and 25 wt%) alloys after long anneals (600–4000 h) was studied between 210 and 440 °C. The transition from incomplete to complete wetting of Al/Al grain boundaries (GBs) by the second solid phase Al₃Mg₂ has been observed. The portion of completely wetted GBs increases with increasing temperature beginning from T _wsmin = 220 °C. Above T _wsmax = 410 °C all Al/Al GBs are completely wetted by the Al₃Mg₂ phase.     

Specific features of the processes of thermal desorption and HDDR in the Zr<Subscript>3</Subscript>FeO<Subscript>x</Subscript>H<Subscript>y</Subscript> system

We study the processes of thermal desorption of hydrogen and hydride disproportionation for the Zr₃FeO_x (x = 0–1.0 ) intermetallic compounds depending on the amount of oxygen. As the oxygen content of the Zr₃FeO_x compounds increases, their susceptibility to disproportionation at room temperature decreases. It is shown that, for the Zr₃FeO_x compounds, the character of thermal desorption of hydrogen in a vacuum and the character of disproportionation in hydrogen at high temperatures strongly depend on the oxygen content. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 81–84, September–October, 2007.     

Effects of post-deposition annealing temperature and ambient on RF magnetron sputtered Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> gate on n-type silicon substrate

Samarium oxide (Sm₂O₃) thin films with thicknesses in the range of 15–30 nm are deposited on n-type silicon (100) substrate via radio frequency magnetron sputtering. Effects of post-deposition annealing ambient [argon and forming gas (FG) (90% N₂ + 10% H₂)] and temperatures (500, 600, 700, and 800 °C) on the structural and electrical properties of deposited films are investigated and reported. X-ray diffraction revealed that all of the annealed samples possessed polycrystalline structure with C-type cubic phase. Atomic force microscope results indicated root-mean-square surface roughness of the oxide film being annealed in argon ambient are lower than that of FG annealed samples, but they are comparable at the annealing temperature of 700 °C (Argon—0.378 nm, FG—0.395 nm). High frequency capacitance–voltage measurements are carried out to determine effective oxide charge, dielectric constant and semiconductor-oxide interface trap density of the annealed oxide films. Sm₂O₃ thin films annealed in FG have smaller amount of effective oxide charge and semiconductor-oxide interface trap density than those oxide films annealed in argon. Current–voltage measurements are conducted to obtain barrier heights of the annealed oxide films during Fowler–Nordheim tunneling.     

Superprotonic CsH<Subscript>2</Subscript>PO<Subscript>4</Subscript>-CsHSO<Subscript>4</Subscript> solid solutions

We have performed partial HSO₄⁻ substitution in CsH₂PO₄ and studied the associated structural changes and the proton conductivity of the resultant (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions in the range x = 0.01–0.3. The results indicate that, at room temperature, the solid solutions are disordered. In the range x = 0.01–0.1, they are isostructural with the low-temperature phase of CsH₂PO₄ (sp. gr. P2₁/m), and their unit-cell parameters increase with x, whereas in the range x = 0.15–0.3 the solid solutions are isostructural with the high-temperature, cubic phase of CsH₂PO₄ (Pm3m), and their unit-cell parameter decreases. The conductivity of the (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions with x ≤ 0.3 depends significantly on their composition and increases at low temperatures by up to four orders of magnitude, approaching that of the superionic phase of CsH₂PO₄ in the range x = 0.15–0.3 because of the hydrogen bond weakening and increased proton mobility. The conductivity of the superionic phase decreases with increasing x by no more than a factor of 1.5–2, and the superionic phase transition, which occurs at 231°C in CsH₂PO₄, shifts to lower temperatures and disappears for x ≥ 0.15. The activation energy for low-temperature conduction decreases with increasing x: from 0.9 eV in CsH₂PO₄ to 0.48 eV at x = 0.1.     

Preparation of Pb(Zr,Ti)O<Subscript>3</Subscript>–Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> piezoelectric ceramics by dry–dry method

Ternary perovskite ceramics of Pb[(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x]_0.98Nb_0.02O_3.01 (PZTMN, x = −0.075, −0.05, −0.025, 0, 0.025, 0.05, and 0.075 ), are synthesized via dry–dry method. B-site precursors of PZTMN ([(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x ]_0.98Nb_0.02O_2.01, ZTMN) can be synthesized via a two-step solid state reaction method. The first calcination temperature is 1,300 °C, and the second is not higher than 1,360 °C. Incorporation of magnesium and niobium ions promotes the formation of the single phase solid solution with ZrTiO₄ structure. Single phase perovskite PZTMN is formed at 780 °C, much lower than that in conventional process. Dense ceramics can be sintered at about 1,260 °C with dielectric and piezoelectric properties comparable to that of wet–dry method and higher than that of conventional method. It seems that B-site precursor method is cost effective in preparation of ternary piezoelectric ceramics.