Hydrogenation of CaLi2−xMgx (0 ≤ x ≤ 2) with C14 Laves phase structure

CaLi_2−xMg_x (0 ≤ x ≤ 2) which has the C14-type Laves phase structure has been successfully synthesized and hydrogenated. The C14-type Laves phase structure was kept after hydrogenation of CaLi_2−xMg_x (x = 0.2, 0.5, 1). After hydrogenation of CaLi₂ and CaMg₂, the Laves phase disappeared. The CaH₂ and LiH phases were formed from CaLi₂ and the CaH₂ and Mg phases from CaMg₂, respectively. CaLi_2−xMg_x (0 < x < 2) ternary alloys formed stable hydride phases with the C14-type Laves phase structure in contrast to CaLi₂ and CaMg₂ binary alloys.     

Self-propagating high-temperature synthesis with post-heat treatment of La1−xSrxFeO3 (x = 0–1) perovskite as catalyst for soot combustion

La_1−xSr_xFeO₃ (x = 0–1) perovskite, Sr-substituted LaFeO₃, was prepared by Self-propagating high-temperature synthesis (SHS) and its catalytic activity for soot combustion was experimentally examined in comparison with that of a conventional Pt/Al₂O₃ catalyst. The products were also characterized by XRD, FE-SEM, and BET specific surface area. The XRD analysis revealed that all the products had a perovskite phase as the major compound, together with intermediate phases with higher x values (x = 0.7–1). The BET specific surface area of the products increased with x. Moreover, the catalytic activity for soot combustion also increased with x, wherein the BET specific surface area appeared an appropriate index for explaining the observed activity. The sample with x = 0.8 exhibited the highest activity for soot combustion among all the SHS products. The soot combustion temperature of this product was as much as 100 °C lower than that of non-catalytic soot combustion. In other words, it had the same activity as that at only 20 °C higher, in comparison to conventional Pt/Al₂O₃ catalyst. More significantly, average apparent activation energy of sample with x = 0.8 calculated by Friedman method using TG/DTA was approximately 15 kJ/mol lower than that of Pt/Al₂O₃ catalyst. This result suggested that La_1−xSr_xFeO₃ has the possibility to be an alternative catalyst to Pt/Al₂O₃ catalyst.     

Structural, magnetic and electrical properties of (La0.70−xNdx)Sr0.30Mn0.70Cr0.30O3 with 0 ≤ x ≤ 0.30

The structural, magnetic and electrical properties of (La_0.70−xNd_x)Sr_0.30Mn_0.70Cr_0.30O₃ perovskites (0 ≤ x ≤ 0.30) prepared by the usual ceramic procedure were investigated. Structural Rietveld refinement revealed that these compounds crystallize in a rhombohedral perovskite structure when x = 0, 0.10 and 0.20, while for x = 0.30 the structure becomes orthorhombic (Pbnm). It was found that the substitution of La by Nd reduces the Curie temperature (T_C). The FC, ZFC, M(H) and AC susceptibility measurements show typical canted-antiferromagnetism for the Nd-doped samples, in which a ferromagnetic component coexists with predominant antiferromagnetic interactions. The values of the magnetization (M(H)) decrease very slightly when increasing the Nd content, compared to the undoped sample (M_S values at 5 T and 2 K are, respectively, 47.9, 47.3 and 47.5 emu/g for x = 0.10, 0.20 and 0.30, compared to 48.2 emu/g for x = 0), indicating that the Nd³⁺ contribution is negligible compared to the total moment of the ferromagnetic (Mn/Cr) network. The resistivity increases by several orders of magnitude with Nd-doping and the semi-conducting behaviour persists in the whole temperature range. The interaction between Mn⁴⁺–O–Cr³⁺and Cr³⁺–O–Cr³⁺ is responsible for the semi-conducting state.     

Structure, microstructure and electrical properties of (1 − x − y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBi0.5Li0.5TiO3 lead-free piezoelectric ceramics

The ternary system (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBi_0.5Li_0.5TiO₃ (abbreviated to BNKLT-x/y) was synthesized by conventional oxide-mixed method. The phase structure, microstructure, and dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. The X-ray diffraction patterns showed that pure perovskite phase with rhombohedral structure can be obtained in all the ceramics. The grain size varied with x and y. The temperature dependence of dielectric constant and dielectric loss revealed there were two phase transitions which were from ferroelectric (tetragonal) to anti-ferroelectric (rhombohedral) and anti-ferroelectric to paraelectric (cubic). Either increasing x or y content can make T_m (the temperature at which dielectric constant _r reaches the maximum) increase. With the addition of Bi_0.5K_0.5TiO₃, the remanent polarization P_r increased but the coercive field E_c decreased. With the addition of Bi_0.5Li_0.5TiO₃, P_r increased obviously and E_c increased slightly. Due to the stronger ferroelectricity by modifying Bi_0.5K_0.5TiO₃ and Bi_0.5Li_0.5TiO₃, the piezoelectric properties were enhanced at x = 0.22 and y = 0.10, which were as follows: P_r = 31.92 μC/cm², E_c = 32.40 kV/cm, _r = 1118, tan δ = 0.041, d₃₃ = 203 pC/N and K_p = 0.31. The results show that the BNKLT-x/y ceramics are promising candidates for the lead-free materials.     

Dielectric and magnetic properties of 0.7Bi(Fe1−xCrx)O3–0.1BaTiO3–0.2PbTiO3 solid solutions

0.7Bi(Fe_1−xCr_x)O₃–0.1BaTiO₃–0.2PbTiO₃ (x = 0, 0.1, 0.2, 0.3) solid solutions were prepared by the traditional ceramic process. X-ray diffraction results revealed that the samples with x = 0–0.3 showed pure perovskite structure. Frequency and temperature dependences of dielectric constants and dielectric loss of the samples were investigated. Both dielectric constant and the loss tangent increased at given frequencies (100 Hz–1 MHz), while the Curie temperature of the solid solutions decreased with increasing Cr content. Room temperature magnetic hysteresis loops indicated that an appropriate amount of Cr could improve magnetization of the solid solutions.     

Studies on structural and thermal expansion properties of Ho2−xLnxMo4O15 (Ln = Er, Sm and Ce) solid solutions

Three new series of Ho_2−xEr_xMo₄O₁₅ (x = 0.0–2.0), Ho_2−xSm_xMo₄O₁₅ (x = 0.0–0.6) and Ho_2−xCe_xMo₄O₁₅ (x = 0.0–0.25) solid solutions have been prepared successfully by solid-state reaction and studied by powder X-ray diffraction. All the XRD patterns of these molybdates can be indexed in monoclinic space group P2₁/c. Lattice parameters a, b and c of Ho_2−xLn_xMo₄O₁₅ decrease linearly with increasing erbium content and increase with increasing samarium or cerium content. Thermal expansion behaviors of Ho_2−xLn_xMo₄O₁₅ have been investigated in the 25–500 °C temperature range with high-temperature X-ray diffraction. The temperature dependence of Mo(2)–O14 interaction looks like to be responsible for their thermal expansion behaviors.     

Influence of Co substitution on magnetoelastic properties of Er2Fe14−xCoxB (x = 1, 3 and 5) intermetallic compounds

The magnetostriction and thermal expansion of Er₂Fe_14−xCo_xB (x = 1, 3 and 5) intermetallic compounds were measured, using the strain gauge method in the temperature range 75–450 K under applied magnetic fields up to 1.5 T. For all samples the longitudinal magnetostriction (λ_l) undergoes an anomaly around the spin reorientation temperature (T_SR). It is also observed that λ_l decreases with increasing the Co content. All compounds show saturation type behaviour in their anisotropic magnetostriction curves at different temperatures and applied fields. The saturation behaviour of the compound with x = 3 occurs at higher temperatures than with x = 1 and 5. The volume magnetostriction strongly increases below μ₀H = 0.3 T, then monotonically rises with applied field up to the spin reorientation temperature. An invar type behaviour is observed above 200 K in the compound with x = 1. The results are discussed based on the temperature dependence of magnetocrystalline anisotropy of compounds below and above their T_SR.     

Study of (1 − x)(Mg0.6Zn0.4)0.95Co0.05TiO3–xCa0.61Nd0.26TiO3 microwave dielectrics

The microwave dielectric properties and the microstructures of the (1 − x)(Mg_0.6Zn_0.4)_0.95Co_0.05TiO₃–xCa_0.61Nd_0.26TiO₃ ceramic system were investigated. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. Ca_0.61Nd_0.26TiO₃ has a large positive temperature coefficient of resonant frequency. (Mg_0.6Zn_0.4)_0.95Co_0.05TiO₃ possesses a negative temperature coefficient of resonant frequency. By appropriately adjusting the x value in the (1 − x)(Mg_0.6Zn_0.4)_0.95Co_0.05TiO₃–xCa_0.61Nd_0.26TiO₃ ceramic system, a near-zero τ_f value can be obtained. A new microwave dielectric material of 0.8(Mg_0.6Zn_0.4)_0.95Co_0.05TiO₃–0.2Ca_0.61Nd_0.26TiO₃ possesses the excellent dielectric properties of a dielectric constant of 28.6, a Q × f value of 80,600 GHz and a temperature coefficient of resonant frequency of 4.1 ppm/°C and has a lower sintering temperature of 1250 °C.     

Phase transition-induced high electromechanical activity in [(K0.5Na0.5)1−xLix](Nb0.8Ta0.2)O3 lead-free ceramic system

A high electromechanical activity is observed in the [(K_0.5Na_0.5)_1−xLi_x](Nb_0.8Ta_0.2)O₃ (x = 0, 0.02, and 0.03) lead-free ceramic system at and around the orthorhombic (O)–tetragonal (T) phase transition temperature (T_O–T). This activity is found to originate from an O–T phase transition region at ambient temperature rather than a classical morphotropic phase boundary (MPB) region intrinsic in the Pb(Zr_1−xTi_x)O₃ (PZT) lead-based ceramic system. Li modification enables a large decrease in T_O–T instead of constituting a classical MPB. In contrast to the nearly temperature-independent classical MPB behavior in the PZT system, the strong temperature-dependent phase transition behavior in the system may impose a challenge to temperature demanding applications.     

Effect of Yb substitution on microstructure, physical and mechanical properties of negative thermal expansion Zr1−xYbxWMoO8−x/2 (x = 0–0.05) ceramic

Cubic Zr_1−xYb_xWMoO_8−x/2 (x = 0–0.05) ceramic was first fabricated by a polymorphous precursor transition method. X-ray diffraction experiment indicates that samples with x ≤ 0.05 are single phase solid solution. The measured bulk density, microstructure, maximal compression strength and Young's modulus are obviously sensitive to Yb substitution level, while none of such sensitivity was found for the lattice parameters, negative thermal expansion coefficients and Vickers hardness. Drilling tests on Zr_0.96Yb_0.04WMoO_7.98 ceramic indicate good machinability, which is often required for quality and shape control in engineering applications.     

Structural, electrical and magnetic properties of Cu1−xZnxFe2O4 ferrites (0 ≤ x ≤ 1)

Copper–zinc ferrites bearing chemical formula Cu_1−xZn_xFe₂O₄ for x ranging from 0.0 to 1.0 with the step increment of 0.2 were prepared by the standard solid-state technique. The variation of Zn substitution has a significant effect on the structural, electrical and magnetic properties. Lattice parameters ‘a’ increased from 8.370 to 8.520 Å. Dielectric constant decreased up to 311 with the increase in frequency from 80 Hz to 1 MHz at room temperature. All the samples follow the Maxwell–Wagner's interfacial polarization. Saturation magnetization, magnetic moment and Yafet–Kittel angles were also determined. The possible reasons responsible for the change in density related, electrical and magnetic properties with the increase in Zn concentration are undertaken.     

Martensitic transformation and anomalies in resistivity of (Ti–50Ni)1−xCx (x = 0.1, 0.5 at.%) shape memory alloys

Phase transformation of solid solution (Ti–50Ni)_1−xC_x (x = 0.1, 0.5 at.%) alloys have been studied by using differential scanning calorimetry, physical property measurement system and optical microscope. The transformation temperature decreases due to the existence of titanium carbide (TiC) particles compared with that of near-equiatomic Ti–Ni shape memory alloy. The resistivity vs. temperature curves show hysteresis. Thermoelastic martensitic transformation occurred in two alloys despite the difference in TiC content. Nevertheless, the resistivity results show different martensitic transformation routes. A one-step B2 → B19′ transformation occurred in the low TiC content alloy and an R transformation appeared in another alloy, suggesting that the martensitic transformation routes depended on the TiC content. The cumulative effect of the TiC particles causes the local stress field and lattice distortion to restrain the transformation of the B19′. On the other hand, the TiC content has an effect on the temperature coefficient of electrical resistivity (TCR) of alloys. The Ti–Ni–0.5C alloy shows a negative TCR in the range 100–300 K during which transformation occurs. Another alloy shows the opposite result. The cause of the negative TCR is briefly discussed.     

Investigation on the structures and electrochemical performances of La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.2) electrode alloys prepared by melt spinning

In order to improve the electrochemical cycle stability of the La–Mg–Ni system A₂B₇-type electrode alloys, La in the alloy was partially substituted by Zr and the melt-spinning technology was used for preparing La_0.75−xZr_xMg_0.25Ni_3.2Co_0.2Al_0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results obtained by XRD, SEM and TEM showed that the as-cast and quenched alloys have a multiphase structure which is composed of two main phases (La, Mg)Ni₃ and LaNi₅ as well as a residual phase LaNi₂. The substitution of Zr for La leads to an obvious increase of the LaNi₅ phase in the alloys, and it also helps the formation of a like amorphous structure in the as-quenched alloy. The results of the electrochemical measurement indicated that the substitution of Zr for La obviously decreased the discharge capacity of the as-cast and quenched alloys, but it significantly improved their cycle stability. The discharge capacity of the alloys (x ≤ 0.1) first increased and then decreased with the variety of the quenching rate. The cycle stability of the alloys monotonously rose with increasing quenching rate.     

Structure and magnetic properties of Gd3(Fe1−xTix)29 (x=0.011–0.034)

Single-phase compounds Gd₃(Fe_1−xTi_x)₂₉ (x=0.0110.034) have been synthesized. Gd₃(Fe_1−xTi_x)₂₉ crystallises in a monoclinic lattice with space group P2₁/c, and the crystal structure is refined by the Rietveld technique based on X-ray powder diffraction data. Thermomagnetic analysis indicates that the Curie temperature of the compounds ranges from 517 K to 538 K. The saturation magnetizations of the Gd₃(Fe_1−xTi_x)₂₉ (x=0.011, 0.022, 0.034) at 1.5 K are 103.6, 102.0 and 94.3 Am²/kg, and the anisotropy fields at 1.5 K are 6.0, 6.2 and 6.4T, respectively.     

Electrical behaviour of hydridofluorides of potassium–calcium KCaH3−xFx with x = 1, 1.5, 2, 2.5

This paper reports the results of the electrical conductivity measurements for KCaH_3−xF_x series with (x = 1, 1.5, 2, 2.5) in the temperature range 298–503 K.The activation energy of the electrical conductivity for the studied compounds depends on hydrogen amount and Reau's criteria. Differential thermal analysis curves were measured in the same temperature range 298–503 K.Possible correspondence between preferential order given by X-ray diffraction, thermal behaviour and electrical properties are discussed.     

Formation and properties of the Zr75−xAlxNi10Cu10Ti5 bulk metallic glasses

Zr-based bulk metallic glasses (BMGs) exhibit interesting mechanical properties since they combine high fracture stress, elastic strain (up to 2%), significant fracture toughness and good corrosion resistance. Quaternary systems with general composition Zr–Ni–Cu–Ti show wide composition ranges in which BMG can be obtained. The addition of the another element to the quaternary alloys often increases the glass forming ability (GFA). The aim of this work was to study the influence of aluminium content on the GFA and on the mechanical properties of the Zr–Ni–Cu–Ti alloys. Multicomponent Zr_75−xAl_xNi₁₀Cu₁₀Ti₅ (x = 15, 20 at%) alloys were produced by melt spinning method obtaining ribbons, and by casting technique into a copper mould, manufacturing rod shape samples with maximum diameter of 2 mm. Supercooled liquid region depends on chemical composition and exceeds 45 °C. Vickers microhardness of studied alloys is comparable to the highest ones for other Zr-based BMG.     

Characterization of phases in complex metallic alloys Al73Mn27−xFex (x = 2, 4 and 6)

The characterization of phases in Al₇₃Mn_27−xFe_x (x = 2, 4 and 6) alloys was performed using X-ray diffraction, differential thermal analysis, and scanning electron microscopy enabling energy dispersive X-ray spectroscopy. Both the annealed and the thermally cycled states were studied. In the annealed states the occurrence of T-phase was expected, however it was confirmed for alloys Al₇₃Mn₂₅Fe₂ and Al₇₃Mn₂₃Fe₄ only. The annealing of the Al₇₃Mn₂₁Fe₆ alloy probably led to the formation of decagonal quasicrystal (D). The T- and D-phases were found to be unstable at low temperatures. In the states after DTA the low temperature Al₁₁(Mn,Fe)₄ and γ₂ phases were observed in the Al₇₃Mn₂₅Fe₂ and Al₇₃Mn₂₁Fe₆ alloys, while only the former phase was observed in the Al₇₃Mn₂₃Fe₄ alloy.     

X-ray diffraction study of Ba0.985Na0.015Ti0.985Nb0.015O3, Ba0.6Na0.4Ti0.6Nb0.4O3 and Ba0.3Na0.7Ti0.3Nb0.7O3 compositions

The Ba_0.985Na_0.015Ti_0.985Nb_0.015O₃, Ba_0.6Na_0.4Ti_0.6Nb_0.4O₃ and Ba_0.3Na_0.7Ti_0.3Nb_0.7O₃ compositions of the (1 − x) BaTiO₃–xNaNbO₃ (BTNNx) system have been studied by X-ray diffraction and by measurements of dielectric properties. The specimens with composition BTNN (x = 0.015, 0.40 and 0.70) have been refined by the JANA program from X-ray powder diffraction data. Ceramic samples with composition (1 − x) BaTiO₃ + xNaNbO₃ (where x = 0.015, 0.40 and 0.70) were prepared by calcinations from appropriate mixture of BaCO₃, TiO₂, Na₂CO₃ and Nb₂O₅. The calcined powder was sintered at temperature range 1200–1400 °C. As the composition x increased from 0.015 (and 0.70), the ferroelectric ceramics (x = 0.015, FE) with tetragonal phase changed to the ferroelectric relaxors (RFE, x = 0.40). RFE ceramics showed a peculiar diffuse phase transition and dielectric relaxation at the low temperature (down to 180 K) due to a frustration between RFE and FE state. These ceramics present the classical ferroelectric character when 0 ≤ x < 0.075 and 0.55 < x ≤ 1 and relaxor character when 0.075 ≤ x ≤ 0.55.     

Magnetic ordering and magnetic properties of ErAuxNi1−xIn (0 ≤ x ≤ 1) solid solution

The ErAu_xNi_1−xIn (0 ≤ x ≤ 1) quasiternary compounds crystallize in the hexagonal layered crystal structure of ZrNiAl-type. ErAuIn was reported to be an antiferromagnet with T_N = 3 K and magnetic moments having triangular arrangement within the basal plane (the magnetic order is described by the propagation vector ). On the contrary ErNiIn is a ferromagnet with T_C = 9 K and magnetic moments pointing along the c-axis. The magnetic ordering in ErAu_xNi_1−xIn (0 < x < 1) solid solution, has been investigated by neutron diffractometry in the temperature range between 1.5 and 15 K. Moreover, bulk magnetic measurements have been carried out in the range 1.72–400 K. All alloys of intermediate composition were found to be antiferromagnets with T_N between 4.6 and 7 K. Below 2 K their magnetic order is described by the propagation vector and magnetic moments are aligned along the c-axis. However, for alloys with 0.2 ≤ x ≤ 0.7 the propagation vector was found to turn into with increasing temperature.     

Structural and piezoelectric properties of LiNbO3-modified BiScO3–PbTiO3 ceramics

Piezoelectric perovskite materials based on the solid solution (1 − x)BiScO₃–xPbTiO₃ (BSPT) have been attracting attention for their high Curie temperature (T_c = 450 °C) and excellent piezoelectric properties. The LiNbO₃ (LN), which has a T_c as high as 1150 °C, has been recently reported forming a phase pure perovskite solid solution with some perovskite structure compounds. In the current work, the effects of LN substitution on the structural and electrical properties of BSPT ceramics were investigated in the 0.36BiScO₃–0.64{(1 − x)PbTiO₃–xLiNbO₃} (BSPTLNx) system. The results of LN addition in the BSPT ceramics show significant enhancement of the piezoelectric properties. The piezoelectric constant d₃₃, planar electromechanical coupling coefficient and remnant polarization P_r values reached 465 pC/N, 0.57 and 48 μC/cm², respectively, for x = 0.04. The T_c gradually decreases with increasing LN content in the BSPTLNx system, due to the structure transform from the tetragonal to the rhombohedral. A typical relaxor behavior is also produced with the LN substitution in the BSPTLNx system.