Composition dependence of magnetic properties of directly quenched Nd-Fe-Ti-Zr-B bulk magnets

Magnetic properties, phase evolution, and microstructure of directly quenched Nd_yFe_97−y−zTi_3−xZr_xB_z (x = 0-3; y = 7-10; z = 14-19) bulk magnets of 0.9 mm in diameter have been investigated. Proper Zr substitution for Ti and appropriate Nd and B contents modify the magnetic phases constitution and refine the grain size from 200-250 nm to 50-100 nm. Consequently, the magnetic properties of the rods are enhanced remarkably from _iH_c = 6.2 kOe and (BH)_max = 5.6 MGOe for Zr-free rods to _iH_c = 6.7-13.5 kOe and (BH)_max = 6.7-8.2 MGOe for Zr-substituted Nd_yFe_97−y−zTi_3−xZr_xB_z rods (x = 0.5-2; y = 8-10; z = 14-16). The optimum magnetic properties of B_r = 6.6 kG, _iH_c = 9.6 kOe and (BH)_max = 8.2 MGOe were achieved for Nd_9.5Fe_72.5Ti_2.5Zr_0.5B₁₅ alloy.     

High-Q microwave dielectrics in the (Mg1−xZnx)Al2O4 (x = 0-0.1) system

The microwave dielectric properties and the microstructures of (Mg_1−xZn_x)Al₂O₄ (x = 0-0.1) ceramic system prepared by the conventional solid-state route were investigated. The forming of spinel-structured (Mg_1−xZn_x)Al₂O₄ (x = 0-0.1) solid solutions was confirmed by the XRD patterns and the measured lattice parameters, which linearly varied from a = b = c = 8.0815 Å for MgAl₂O₄ to a = b = c= 8.0828 Å for (Mg_0.9Zn_0.1)Al₂O₄. By increasing x, the Q × f of (Mg_1−xZn_x)Al₂O₄ can be tremendously boosted from 82,000 GHz at x = 0 to a maximum of 156,000 GHz at x = 0.05. The Zn substitution was effective in reducing the dielectric loss without detrimental effects on the ?_r and τ_f values of the ceramics.     

Interstitial solid solution Hf5GaxSn3 (x = 0-1)

Formation of an interstitial solid solution Hf₅Ga_xSn₃ (x = 0-1) based on the binary compound Hf₅Sn₃ (structure type Mn₅Si₃, Pearson symbol hP16, space group P6₃/mcm, a = 8.36562(6), c = 5.70775(4) Å from X-ray powder diffraction) was established at 600 °C. The crystal structure (structure type Hf₅CuSn₃, ordered derivative of Ti₅Ga₄, hP18, P6₃/mcm) was refined on X-ray single-crystal diffraction data for three compositions: Hf₅Ga_0.16(3)Sn₃ (a = 8.3288(12), c = 5.6988(11) Å), Hf₅Ga_0.53(2)Sn₃ (a = 8.4205(12), c = 5.7655(12) Å) and Hf₅GaSn₃ (a = 8.5564(12), c = 5.7859(12) Å). The Ga atoms occupy Wyckoff position 2b at the centres of Hf₆ octahedral interstices.     

Structure and electrical properties of MnO2-doped Sr2−xCaxNaNb5O15 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics Sr_2−xCa_xNaNb₅O₁₅ + y wt% MnO₂have been prepared by the conventional solid state reaction method. Our results reveal that Ca²⁺and Mn ions have entered into the Sr₂NaNb₅O₁₅ lattices to form a solid solution with tungsten-bronze structure. The substitution of Ca²⁺ induces a decrease in piezoelectric coefficient d₃₃, electromechanical coupling factors k_p and k_t, while, the addition of Mn ions decreases the sintering temperature and effectively promotes the densification of the ceramics. The effect of substitution of Ca²⁺and Mn ions on the structure, electrical properties and diffused phase changing were investigated systematically. For the ceramic with x = 0.05 and y = 0.5, the piezoelectric, dielectric and ferroelectric properties become optimum, giving a piezoelectric coefficient d₃₃ = 190 pC/N, electromechanical coupling factors k_p = 13.4% and k_t = 36.5%, ?_r = 2123, loss tangent tan δ = 0.038, remanent polarization P_r = 4.76 μC/cm², coercive field E_c = 12.68 kV/cm, and Curie temperature T_c = 260 °C.     

The Al-rich region of the Al-Mn-Ni alloy system. Part II. Phase equilibria at 620-1000 °C

Phase equilibria in the Al-rich region of the Al-Mn-Ni alloy system were studied at 1000, 950, 850, 750, 700, 645 and 620 °C. Three ternary thermodynamically stable intermetallics, the φ-phase (Al₅Co₂-type, hP26, P6₃/mmc; a = 0.76632(16), c = 0.78296(15) nm), the κ-phase (κ-Al_14.4Cr_3.4Ni_l.1-type, hP227, P6₃/m; a = 1.7625(10), c = 1.2516(10) nm), and the O-phase (O-Al₇₇Cr₁₄Pd₉-type, Pmmn, oP650,: a = 2.3316(16), b = 1.2424(15), c = 3.2648(14) nm), as well as three ternary metastable phases, the decagonal D₃-phase with periodicity about 1.25 nm, the Al₉(Mn,Ni)₂-phase (Al₉Co₂-type, P112₁/a, mP22; a = 0.8585(16), b = 0.6269(9), c = 0.6205(11) nm, β = 95.34(10)°) and the O₁-phase (base-centered orthorhombic, a ≈ 23.8, b ≈ 12.4, c ≈ 32.2 nm) were revealed. Their physicochemical behaviour in the Al-Mn-Ni alloy system was studied.     

The Al-rich region of the Al-Mn-Ni alloy system. Part I: Ternary phases at 750-950 °C

Ternary phases in the Al-rich region of the Al-Mn-Ni alloy system were studied at 950, 850 and 750 °C. Two new ternary intermetallic compounds were revealed: the φ-phase (Al₅Co₂-type, hP26, P6₃/mmc: a = 0.76632(16) and c = 0.78296(15) nm) and the κ-phase (κ-Al_14.4Cr_3.4Ni_l.1-type, hP227, P6₃/m: a = 1.7625(10) and c = 1.2516(10) nm). The formation of the O-phase (Pmmn; oP650; O-Al₇₇Cr₁₄Pd₉-type; a = 2.3316(16), b = 1.2424(15) and c = 3.2648(14) nm) was confirmed and its chemical composition as well as thermodynamic stability was specified.     

Microstructure and room temperature properties of a high-entropy TaNbHfZrTi alloy

A new refractory alloy, Ta₂₀Nb₂₀Hf₂₀Zr₂₀Ti₂₀, produced by vacuum arc-melting followed by hot isostatic pressing (HIPing) at T = 1473 K and P = 207 MPa for 3 h has predominantly a single-phase body-centered cubic (BCC) structure with the lattice parameter a = 340.4 pm. The alloy density and Vickers microhardness are ρ = 9.94 g/cm³ and H_v = 3826 MPa. The alloy has high compression yield strength (σ_0.2 = 929 MPa) and ductility (? > 50%). The alloy shows considerable strain hardening and homogeneous deformation. A simple model of solid-solution strengthening is proposed to explain the behavior.     

Phase structure and electrical properties of (0.8 − x) BaTiO3-0.2Bi0.5Na0.5TiO3-xBaZrO3 lead-free piezoceramics

Lead-free piezoelectric ceramics (0.8 − x)BaTiO₃-0.2Bi_0.5Na_0.5TiO₃-xBaZrO₃ (BT-BNT-xBZ, 0 ≤ x ≤ 0.08) doped with 0.3 wt% Li₂CO₃ were prepared by conventional solid-state reaction method. With the Li₂CO₃ doping, all the ceramics can be well sintered at 1170-1210 °C. The phase structure, dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. Results show that a morphotropic phase boundary (MPB) between tetragonal and pseudocubic phases exists at x = 0.03-0.04. The addition of Zr can improve the piezoelectric properties of BT-BNT ceramics. Furthermore, a relaxor behavior is induced and the tetragonal-cubic phase transition shifts towards lower temperatures after the addition of Zr. The ceramics with x = 0.03 possess the optimum electrical properties: d₃₃ = 72 pC/N, k_p = 15.4%, ?_r = 661, P_r = 18.5 μC/cm², E_c = 34.1 kV/cm, T_c = 150 °C.     

Comparison of dehydriding kinetics between pure LaNi5 and its substituted systems

The kinetic mechanisms of dehydriding reaction in La_0.8M_0.2Ni₅ and LaNi_4.5T_0.5 were comparatively investigated by the Chou model and the first order model, and the former was superior to the latter from the comparison of theoretical calculated results and experimental data. According to the characteristic time (t_c) in the Chou model, substituting La (t_c = 71.36 s) with Ce (t_c = 35.64 s), Nd (t_c = 30.82 s) and Pr (t_c = 28.86 s) increased the dehydriding reaction rate, but partial substitution of Ni (t_c = 71.36 s) with Co (t_c = 102.29 s), Fe (t_c = 116.70 s) and Cu (t_c = 120.62 s) decreased the hydrogen desorption reaction rate. The Chou model was also used to discuss the effect of different amount of Ni substituted with Fe and Co. The dehydriding reaction rates of La(Ni_1−xFe_x)₅ increased with x leveling from 0 to 0.20 but decreased with x increasing from 0.20 to 0.30, while that of LaNi_5−yCo_y decreased with increasing the amount of Co from 0 to 3.00. In addition, the Chou model was successfully applied to predicting the kinetic properties of LaNi_4.8Sn_0.2 at 40 °C and 60 °C, which exhibited an excellent agreement with the experimental data.     

High-speed deposition of Y-Si-O films by laser chemical vapor deposition using Nd:YAG laser

Y-Si-O films were prepared by laser chemical vapor deposition (LCVD) with a Nd:YAG laser using TEOS (tetraethyl orthosilicate) and Y(dpm)₃ precursors. The effects of laser power (P_L), deposition temperature (T_dep) and total chamber pressure (P_tot) on the phase, microstructure and deposition rate of Y-Si-O films were investigated. At P_L < 102 W (T_dep < 1140 K), amorphous Y-Si-O films were obtained independent of P_tot. At P_tot = 0.6 kPa, mixture phase films of Y₂SiO₅ (the X1 phase) and Y₂Si₂O₇ (the α, β, δ and y phases) were obtained at P_L = 102 W (T_dep = 1210 K), while single phase X1-Y₂SiO₅ films were prepared at P_L > 139 W (T_dep > 1280 K). Y₂Si₂O₇ mixture phase films were obtained at P_tot = 3.5 kPa and Y₂Si₂O₇ and Y₂SiO₅ (the X2 phase) mixture phase films were obtained at P_tot = 7.5 kPa independent of T_dep. Amorphous Y-Si-O films showed a dense, glassy microstructure. Faceted columnar grains grew on the Y-Si-O films at P_tot = 0.6 kPa, whereas rounded cauliflower-like grains grew at P_tot = 7.5 kPa. The R_dep increased with increasing P_L and T_dep and reached a maximum of 430 μm h⁻¹ at P_tot = 0.6 kPa, P_L = 186 W and T_dep = 1310 K.     

Synthesis, crystal structures, and optical properties of NaCdPnS3 (Pn = As, Sb)

Two compounds NaCdPnS₃ (Pn = As (1), Sb (2)) were synthesized as transparent yellow and red platelets by reacting cadmium powder with the molten mixtures of Na₂S/As₂S₃/S and Na₂S/Sb/S at 500 °C. Both compounds are plagued with crystal twinning and acceptable crystal structure refinement could only be obtained by identifying the type of the twinning laws. NaCdAsS₃ (1) crystallizes in the monoclinic space group P2₁/n (no. 14) with a = 5.6561(8), b = 16.5487(15), c = 5.6954(8) Å, β = 90.315(11)°, and Z = 4. NaCdSbS₃ (2) crystallizes in the monoclinic space group C2/c (no. 15) with a = 8.1329(6), b = 8.1296(4), c = 17.2600(13) Å, β = 103.499(6)°, and Z = 8. The structures of both compounds feature a ²_∞[CdPnS₃]⁻ layer composed of [CdS₄] tetrahedra and [AsS₃] or [SbS₃] pyramidal units. Between the ²_∞[CdPnS₃]⁻ (Pn = As, Sb) layers the Na⁺ cations reside in a distorted octahedral environment of S atoms. Compound 1 is characterized with UV/Vis diffuse reflectance spectroscopy and IR and Raman spectra.     

Electrochemical hydrogen storage properties of non-stoichiometric La0.7Mg0.3−xCaxNi2.8Co0.5 (x = 0-0.10) electrode alloys

The microstructure and electrochemical hydrogen storage characteristics of La_0.7Mg_0.3−xCa_xNi_2.8Co_0.5 (x = 0, 0.05 and 0.10) alloys prepared by arc-melting and subsequent powder sintering method are investigated. The electrochemical measurement results show that the cycle stability after 100 charge/discharge cycles first increases from 46.4% (x = 0) to 54.3% (x = 0.05), then decreases to 43.2% (x = 0.10), and the high rate dischargeability increases from 64.5% (x = 0) to 68.5% (x = 0.10) at the discharge current density of 1200 mA/g. The electrochemical impedance spectroscopy analysis indicates that the electrochemical kinetics of the alloy electrodes is improved by increasing Ca. The entire results exhibit that a suitable content of Ca (x = 0.05) can improve the overall electrochemical hydrogen storage characteristics of the alloys.     

Preparation and electrical properties of Bi0.5Na0.5TiO3-BaTiO3-KNbO3 lead-free piezoelectric ceramics

Lead-free (1 − x)Bi_0.47Na_0.47Ba_0.06TiO₃-xKNbO₃ (BNBT-xKN, x = 0-0.08) ceramics were prepared by ordinary ceramic sintering technique. The piezoelectric, dielectric and ferroelectric properties of the ceramics are investigated and discussed. The results of X-ray diffraction (XRD) indicate that KNbO₃ (KN) has diffused into Bi_0.47Na_0.47Ba_0.06TiO₃ (BNBT) lattices to form a solid solution with a pure perovskite structure. Moderate additive of KN (x ≤ 0.02) in BNBT-xKN ceramics enhance their piezoelectric and ferroelectric properties. Three dielectric anomaly peaks are observed in BNBT-0.00KN, BNBT-0.01KN and BNBT-0.02KN ceramics. With the increment of KN in BNBT-xKN ceramics, the dielectric anomaly peaks shift to lower temperature. BNBT-0.01KN ceramic exhibits excellent piezoelectric properties and strong ferroelectricity: piezoelectric coefficient, d₃₃ = 195 pC/N; electromechanical coupling factor, k_t = 58.9 and k_p = 29.3%; mechanical quality factor, Q_m = 113; remnant polarization, P_r = 41.8 μC/cm²; coercive field, E_c = 19.5 kV/cm.     

Properties of praseodymium-doped bismuth potassium titanate (Bi0.5K0.5TiO3) synthesised using the soft combustion technique

Bismuth potassium titanate (Bi_0.5K_0.5TiO₃; BKT) and praseodymium-doped BKT (Bi_0.5(1−x)Pr_xK_0.5TiO₃; BPKT) powders were synthesised using the soft combustion technique. Fine particles of 10-100 nm of BKT and BPKT were produced. A single phase BKT was obtained with a minimum of 0.5 mol of glycine. Various compounds of Bi_0.5(1−x)Pr_xK_0.5TiO₃ where x = 0.01, 0.03, 0.05, 0.10, 0.15 and 0.20 were prepared. Pure BKT and BPKT powders were obtained after calcination at 800 °C for 3 h. After sintering at 1050 °C for 5 h, pure BKT and BPKT pellets were obtained for x = 0 and 0.01. However, for BPKT with x = 0.03, 0.05, 0.10, 0.15 and 0.20, a minor amount of Bi₄Ti₃O₁₂ (BIT) secondary phase was present after sintering at 1050 °C for 5 h. The crystallite size and grain size of all the samples followed similar trends, first increasing from x = 0 (undoped BKT) to x = 0.05 and then decreasing above x = 0.05. Among the undoped and doped samples, BPKT with x = 0.05 had the highest dielectric properties (?_r = 713.87) due to its large crystallite size (68.66 nm), large grain size (∼435 nm) and high relative density (93.39%).     

Negative magnetization, magnetic anisotropy and magnetic ordering studies on Al-substituted copper ferrite

Detailed magnetic properties of Al³⁺-modified CuFe₂O₄ spinel ferrite system: CuAl_xFe_2−xO₄; x = 0.0, 0.2, 0.4 and 0.6, have been studied by means of X-ray powder diffraction, field cooled (FC) and zero field cooled magnetization (ZFC) (H = 10 mTesla, T = 4-325 K), magnetic hysteresis (H_max = 2 Tesla, T = 10 and 300 K) and low field (40 A/m) ac susceptibility (T = 300-750 K) measurements. The system exhibits canted spin structure. It has been shown that the observed features of the FC-ZFC magnetization and ac susceptibility curves arise due to the low magneto crystalline anisotropy, not due to the cluster spin-glass-like magnetic ordering. The interesting features like low temperature cusp in the ZFC magnetization for all the compositions and negative magnetization for x = 0.6 composition have been observed. An attempt has been made to explain the negative magnetization within the framework of available models.     

Preparation and characterization of barium titanate stannate solid solutions

BaSn_xTi_1−xO₃ (x = 0; 0.05; 0.1; 0.15; 0.2) solid solutions were prepared via conventional solid state reaction and sintered at 1300 °C for 4 h, resulting in dense single phase ceramics with homogeneous microstructures. Tetragonal symmetry for x ≤ 0.1, cubic for x = 0.2 and a superposition of tetragonal and cubic for x = 0.15 compositions were found by X-ray diffraction analysis. The temperature and frequency dependence of the complex dielectric constant and dc tunability were determined. A transformation from normal ferroelectric to relaxor with diffuse phase transition was observed with increasing the Sn concentration. All the investigated compositions show a relative tunability between 0.55 (for x = 0.2) and 0.74 (for x = 0.1), at a field amplitude of E = 20 kV/cm.     

Microstructure, ferroelectric, and piezoelectric properties of (1 − x − y)Bi0.5Na0.5TiO3-xBaTiO3-yBi0.5Ag0.5TiO3 lead-free ceramics

Lead-free (1 − x − y)Bi_0.5Na_0.5TiO₃-xBaTiO₃-yBi_0.5Ag_0.5TiO₃ (BNT-BT-BAT-x/y, x = 0-0.10, y = 0-0.075) piezoelectric ceramics were synthesized by conventional oxide-mixed method. The microstructure, ferroelectric, and piezoelectric properties of the ceramics were investigated. Results show that a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases of BNT-BT-BAT-x/0.04 ceramics is formed at x = 0.06-0.08. The addition of BAT has no obvious change on the crystal structure of BNT-BT ceramics while it causes the grain size of the ceramics to become more homogenous. Near the MPB, the ceramics with x = 0.06 and y = 0.05-0.06 possess optimum electrical properties: P_r ∼ 42.5 μC/cm², E_c ∼ 32.0 kV/cm, d₃₃ ∼ 172 pC/N, k_p ∼ 32.6%, and k_t ∼ 52.6%. The temperature dependences of k_p and polarization versus electric hysteresis loops reveal that the depolarization temperature (T_d) of BNT-BT-BAT-0.06/y ceramics decreases with increasing y. In addition, the polar and non-polar phases may coexist in the BNT-BT-BAT-x/y ceramics above T_d.     

Synthesis, thermal stability and properties of [(Fe1−xCox)72Mo4B24]94Dy6 bulk metallic glasses

A series of [(Fe_1−xCo_x)₇₂Mo₄B₂₄]₉₄Dy₆ (x = 0.1, 0.2, 0.3, 0.4 and 0.5 at.%) bulk metallic glasses (BMGs) in rod geometries with critical diameter up to 3 mm were fabricated by copper mold casting method. This alloy system exhibited good thermal stability with high glass transition temperature (T_g) 860 K and crystallization temperature (T_x) 945 K. The addition of Co was found to be effective in adjusting the alloy composition deeper to eutectic, leading to lower liquidus temperature (T_l). The [(Fe_0.8Co_0.2)₇₂Mo₄B₂₄]₉₄Dy₆ alloy showed the largest supercooled liquid region (ΔT_x = T_x − T_g = 92 K), reduced glass transition temperature (T_rg = T_g/T_l = 0.622) and gamma parameter (γ = T_x/(T_g + T_l) = 0.424) among the present system. Maximum compressive fracture strength of 3540 MPa and micro-Vickers hardness of 1185 kg/mm² was achieved, resulting from the strong bonding structure among the alloy constituents. The alloy system possessed soft magnetic properties with high saturation magnetization of 56.61-61.78 A m²/kg and coercivity in the range of 222-264.2 A/m, which might be suitable for application in power electronics devices.     

Structure and electrical conduction behavior of LiZnVO4 ceramic prepared by solution-based chemical route

In the present work, an evaluation of the structural and electrical properties of a compound (LiZnVO₄) has been undertaken. This compound was prepared by solution-based chemical route. The electrical properties were measured using a.c. impedance spectroscopy method in the frequency range of 10³-10⁶ Hz at various temperatures from 28 to 300 °C. X-ray diffraction study indicates a rhombohedral unit cell structure with lattice parameters a = 14.1934 Å, b = 14.1934 Å, c = 9.4926 Å, V = 1656.12 (Å)³, α = 90°, β = 90° and γ = 120°. A field emission scanning electron micrograph reveals a polycrystalline texture of the compound with grains of unequal sizes ∼0.2-2.0 μm. The electrical conduction in the material is a thermally activated process due to the bulk effect. Frequency dependence of a.c. conductivity obeys Jonscher's universal law (σ_ac = σ_dc + Aωⁿ).