Substitutionsvarianten von Nickel(II) amid: ternäre amidoniccolate mit Lithium und Caesium Li3Ni4(NH2)11·NH3 und Cs2Ni(NH2)4·NH3

The red substance Li₃Ni₄(NH₂)₁₁·NH₃ crystallizes from liquid ammonia at room temperature when LiNO₃, LiCl or LiBr reacts with Na₂Ni(NH₂)₄ in a pressure-resistant glass vessel. A similar reaction between CsNH₂ and Ni(NH₂)₂ gives orange crystals of Cs₂Ni(NH₂)₄ ·NH₃. X-ray investigations gave the following data: Li₃Ni₄(NH₂)₁₁·NH₃: Pna2₁; fZ = 4; ; ; ; p(X-ray) = 1.942 g cm⁻³; N(F_o² 3σ(F_o²) = 944; N(Variable) = 157; R/R_w = 0.059/0.072. Cs₂Ni(NH₂)₄ · NH₃: P2₁/c; Z = 4; ; ; ; β = 129.96(3)°; p(X-ray = 2.960 g cm⁻³;N(F_o² 3σ(F_o²) = 1488; N(Variable) = 73; R/R_w = 0.045/0.052. The synthesis, thermal behaviour, IR spectroscopic characteristics and crystal structures of the compounds are reported and comparisons made with Ni(NH₂)₂ and other amidonickel(II) compounds.     

The ternary system: H2O–Fe(NO3)3–Co(NO3)2 isotherms −15 and −25 °C

The binary system H₂O–Fe(NO₃)₃ has been investigated at temperature ranging between –25 and 47 °C.The solid–liquid equilibria of the ternary system H₂O–Fe(NO₃)₃–Co(NO₃)₂ were studied at −15 and −25 °C by using a synthetic method based on conductivity measurements which allows all the characteristic points of the isotherms to be determined, and the stable solid phases which appear are respectively: ice, Fe(NO₃)₃·9H₂O, Fe(NO₃)₃·6H₂O, Co(NO₃)₂·9H₂O, Co(NO₃)₂·6H₂O and Co(NO₃)₂·3H₂O.     

Crystal structure of Nax(MoO)5(P2O7)4 studied by synchrotron X-ray diffraction

The crystal structure of sodium pentamolybdyl tetradiphosphate Na_x(MoO)₅(P₂O₇)₄ has been determined from synchrotron diffraction data collected at 293 K on two microcrystals. The compound crystallizes in a monoclinic space group I 1 1 2/a (no. 15, setting 11), with unit cell parameters a = 22.905(3), b = 23.069(2), c = 4.8537(2) Å, γ = 90.641(9)° and a = 22.898(3), b = 23.056(2), c = 4.8551(2) Å, γ = 90.82(1)°, for crystals I and II, respectively. The structure is pseudo-tetragonal, and the crystals are pseudo-merohedrally twinned by 90° rotation around the c-axis. The structure closely resembles the previously reported Li-deintercalated Mo_1.3OP₂O₇ [V.V. Lisnyak, N.V. Stus, P. Popovich, D.A. Stratiychuk, Ya. Filinchuk, V.M. Davydov, J. Alloys Compd. 360 (2003) 81–84]. Comparison of the two structures led us to conclude that the Mo₂ and Mo₃ clusters were erroneously identified in Mo_1.3OP₂O₇. A revised structure of Mo_1.3OP₂O₇ contains a fully occupied oxygen site instead of the 16% occupied Mo(2) site, thus the revised formulae for the Li-deintercalated compound is (MoO)₅(P₂O₇)₄. In both structures, the (MoO)₅(P₂O₇)₄ framework strongly resembles the one in the earlier reported Ag(MoO)₅(P₂O₇)₄, while the location of Na and Ag atoms differ.     

Optical absorption and emission spectra of Tb in hexagonal crystals of Na3[Tb(pyridine-2,6-dicarboxylate)3] · NaClO4 · 10H2O

We have measured and analyzed the polarized orthoaxial luminescence and absorption spectra of Tb³⁺ and Eu³⁺ in single crystals of trigonal Na₃[Ln(dpa)₃]·NaClO₄·10H₂O (dpa = 2,6-pyridinedicarboxylate, the dianion of dipicolinic acid). Differential linear polarization (σvs. π) is measured in the orthoaxial luminescence and absorption spectra. A semiempirically derived energy level scheme is developed for the crystal field components of the Tb³⁺ (⁷F_j (J = 0–6), ⁶D₄, ⁶D₃, ⁵G₈, ⁶L₁₀, ⁶D₂) ⁶G₅) and the Eu³⁺ (⁷F_j (J = 0–6), ⁶D_j (J = 0–3) multiplets.     

The magnetic ordering in the Ho5Si3 and Ho5Ge3 compounds

A neutron diffraction investigation has been performed on the Ho₅Si₃ and Ho₅Ge₃ compounds (hexagonal Mn₅Si₃-type, hP16, P6₃/mcm) to study their magnetic structure. The results prove that these intermetallic phases show a complex sine-modulated type magnetic ordering, both presenting on cooling two subsequent antiferromagnetic orderings (T_N1 and T_N2).Between T_N1 = 24(2) and T_N2 = 16(4) K Ho₅Si₃ shows a first antiferromagnetic ordering of the sine-modulated type with a propagation vector K₁ = [0, 0, ±0.284(1)]; then, below T_N2 the sine-modulated type ordering is conserved, but by the two propagation vectors K₁ = [0, 0, ±0.2773(7)] and K₂ = [±1/5, ±1/5, 0].For Ho₅Ge₃, between T_N1 = 27(2) and T_N2 = 18(4) K, the sine-modulated ordering is realized through the propagation vectors K₁ = [0, 0, ±3/10] and K₂ = [0, 1/2, 0], whilst below T_N2 the ordering takes place with propagation vectors K₁ = [0, 0, ±3/10], K₂ = [0, 1/2, 0], K₃ = [0, 0, ±2/5] and K₄ = [±1/5, ±1/5, 0]. For both the Ho₅Si₃ and Ho₅Ge₃ compounds, the dimensions of the magnetic unit cell are 5a × 5a × 10c times the crystal unit cell of Mn₅Si₃-type.     

Improved high-Q microwave dielectric resonator using ZnO-doped La(Co1/2Ti1/2)O3 ceramics

The microwave dielectric properties and the microstructures of ZnO-doped La(Co_1/2Ti_1/2)O₃ ceramics prepared by conventional solid-state route have been studied. Doped with ZnO (up to 0.75 wt%) can effectively promote the densification of La(Co_1/2Ti_1/2)O₃ ceramics with low sintering temperature. At 1320 °C, La(Co_1/2Ti_1/2)O₃ ceramics with 0.75 wt% ZnO addition possesses a dielectric constant (_r) of 30.2, a Q × f value of 73,000 GHz (at 8 GHz) and a temperature coefficient of resonant frequency (τ_f) of −35 ppm/°C.     

Magnetic properties and magnetic structure of the Mn5Si3-type Tb5Si3 compound

Neutron diffraction and magnetization measurements have been performed on the Tb₅Si₃ compound (hexagonal Mn₅Si₃-type, hP16, P6₃/mcm) to understand its magnetic structure and magnetic properties. The temperature-dependent neutron diffraction results prove that this intermetallic phase shows a complex flat spiral magnetic ordering, presenting three subsequent changes in magnetization at on cooling. However, the magnetization data depict two transitions at 72 K (T_N1) and 55 K (T_N2). The extended temperature range between and over which the neutron diffraction patterns slowly evolve might correspond to the high-temperature antiferromagnetic transition at T_N1 and low-temperature antiferromagnetic transition at T_N2 of the magnetic data. Between Tb₅Si₃ shows a flat spiral antiferromagnetic ordering with a propagation vector K₁ = [0,0, ±1/4]; then, between the flat spiral type ordering is conserved, but by two coexisting propagation vectors K₁ = [0,0, ±1/4] and K₂ = [0,0, ±0.4644(3)]. The terbium magnetic moments arrange in the XY(ab) plane of the unit cell. Below the magnetic component with K₁ = [0,0, ±1/4] vanishes and magnetic structure of Tb₅Si₃ is a flat spiral with K₂ = [0,0, ±0.4644(3)], only. Low field magnetization measurements confirm the occurrence of complex, multiple magnetic transitions. The field dependence of the magnetization indicates a metamagnetic transition at a critical field of 3 T.     

Devitrification phase transformations in amorphous Al85Ni7Gd8 alloy

Non-isothermal devitrification phase transformations in amorphous Al₈₅Ni₇Gd₈ over the temperature range from 100 to 1300 °C were systematically investigated using differential scanning calorimetry (DSC), differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) techniques. Continuous heating DSC scans revealed that the crystallization proceeds through multiple stages. The only crystalline phase formed in the first two stages is fcc-Al, appearing exclusively as dendritic single crystals. A metastable phase (τ_n) is formed in the 3rd stage, and another metastable phase (τ_u) is formed in the 4th stage, together with the equilibrium ternary compound τ₁. The equilibrium “binary” compound M₃Gd (M=Al, Ni) with 0.4 at.% Ni solubility is formed only in the 5th stage. Further heating initiates eutectic melting at 635 °C, followed by other melting events at higher temperatures, until fully liquid when T>919 °C. Isothermal annealing at 260 °C readily induces formation of another metastable phase (τ_m) and fcc-Al. Fcc-Al nanocrystal development and interpretation of isothermal DSC technique is discussed.     

New dielectric material system of La(Mg1/2Ti1/2)O3–Ca0.6La0.8/3TiO3 for microwave applications

The microstructure and microwave dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics system with ZnO additions (0.5 wt.%) investigated by the conventional solid-state route have been studied. Doping with ZnO (0.5 wt.%) can effectively promote the densification and the dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics. 0.6La(Mg_1/2Ti_1/2)O₃–0.4Ca_0.6La_0.8/3TiO₃ ceramics with 0.5 wt.% ZnO addition possess a dielectric constant (_r) of 43.6, a Q × f value of 48,000 (at 8 GHz) and a temperature coefficient of resonant frequency (τ_f) of −1 ppm/°C sintering at 1475 °C. As the content of La(Mg_1/2Ti_1/2)O₃ increases, the highest Q × f value of 62,900 (GHz) for x = 0.8 is achieved at the sintering temperature 1475 °C. A parallel-coupled line band-pass filter is designed and simulated using the proposed dielectric to study its performance.     

Hydrogen diffusion in Sm2Fe17 and Sm2Fe14Ga3 compounds

The short-range and long-range diffusion of hydrogen in Sm₂Fe₁₇ and Sm₂Fe₁₄Ga₃ compounds was investigated by magnetic after-effect (MAE) and thermal desorption spectroscopy (TDS). The substitution of iron by gallium greatly reduces the uptake and diffusion of hydrogen in these compounds. After charging in a high-purity H₂ atmosphere of 0.13 MPa at 570 K for 1 h the H content was determined to be Sm₂Fe₁₇H₅ and Sm₂Fe₁₄Ga₃H_1.3. Sm₂Fe₁₇ shows a hydrogen-induced MAE relaxation maximum at 190 K with a mean activation enthalpy of Q=(0.48±0.02) eV and a pre-exponential factor of

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s. In the case of the Ga-substituted compound this maximum is replaced by a double maximum at 200 and 250 K corresponding to activation ethalpies of (0.52±0.02) eV and (0.64±0.02) eV with a pre-exponential factor of

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s. These relaxation maxima are attributed to the short-range diffusion of hydrogen, since they are absent in the degassed compounds. TDS measurements of Sm₂Fe₁₇H₅ and Sm₂Fe₁₄Ga₃H_1.3 were performed in the temperature range from 291 to 515 K yielding activation enthalpies of Q=(0.59±0.02) eV and Q=(0.75±0.03) eV, respectively. The results are explained by different interstitial sites for hydrogen and the impact on the hydrogen disproportionation process is discussed.     

Hydriding/dehydriding behavior of Mg2CoH5 produced by reactive mechanical milling

Complex Mg₂CoH₅ hydride was obtained by a combined procedure that included a milling stage of a 2Mg–Co mixture under argon followed by reactive mechanical alloying (RMA) under hydrogen, both at room temperature. During RMA, MgH₂ is produced at short milling times (10 h) and Mg₂CoH₅ (50 wt%) after 90 h. Improvement in the yield and the formation times could be associated with both refinement of microstructure and enhancement of intermixing of Mg–Co during pre-milling stage. DSC studies of Mg₂CoH₅ phase produced by RMA show that the starting decomposition temperature is about 205 °C.Absorption and desorption PCIs were determined under static (300 °C) and dynamic (230–330 °C) conditions. An important hysteresis and two plateaus were observed and correlated with formation/decomposition of Mg₂CoH₅ (high-pressure plateau) and Mg₆Co₂H₁₁ (low-pressure plateau) hydrides. For comparing hydrogen sorption kinetics, Mg₂CoH₅ (65 wt%) was also obtained by a sintering method at 410 °C and 6.0 MPa of hydrogen pressure. Absorption was very fast in the temperature range of 150–350 °C, independently of synthesis procedure. However, desorption curves showed a better behavior for RMA powders.MgCo was observed after decomposition of Mg₂CoH₅ under particular thermal treatments, while MgCo₂ phase was not detected. The results of this study reinforce the idea that kinetics factors related with atomic mobility play a key role in the formation of Mg–Co intermetallics.     

Conductivity of a new pyrophosphate Sn0.9Sc0.1(P2O7)1−δ prepared by an aqueous solution method

New pyrophosphate Sn_0.9Sc_0.1(P₂O₇)_1−δ was prepared by an aqueous solution method. The structure and conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ have been investigated. XRD analysis indicates that Sn_0.9Sc_0.1(P₂O₇)_1−δ exhibits a 3 × 3 × 3 super structure. It was found that Sn_0.9Sc_0.1(P₂O₇)_1−δ prepared by an aqueous method is not conductive. The total conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ in open air is 2.35 × 10⁻⁶ and 2.82 × 10⁻⁹ S/cm at 900 and 400 °C respectively. In wet air, the total conductivity is about two orders of magnitude higher (8.1 × 10⁻⁷ S/cm at 400 °C) than in open air indicating some proton conduction. SnP₂O₇ and Sn_0.92In_0.08(P₂O₇)_1−δ prepared by an acidic method were reported fairly conductive but prepared by similar solution methods are not conductive. Therefore, the conductivity of SnP₂O₇-based materials might be related to the synthetic history. The possible conduction mechanism of SnP₂O₇-based materials has been discussed in detail.     

Parallelogram-like microparticles of calcium dihydrogen phosphate monohydrate (Ca(H2PO4)2·H2O) obtained by a rapid precipitation route in aqueous and acetone media

Calcium dihydrogenphosphate monohydrate (Ca(H₂PO₄)₂·H₂O) was prepared by a rapid and simple precipitation method using CaCO₃ and H₃PO₄ in aqueous and acetone media at ambient temperature. The thermal transformation of the synthesized Ca(H₂PO₄)₂·H₂O at 500 °C was obtained to be CaP₂O₆ occurred through the dehydration and the phosphate condensation reactions, as revealed by thermoanalytical techniques (TG/DTG/DTA). The synthesized Ca(H₂PO₄)₂·H₂O and its decomposition product CaP₂O₆ were characterized by X-ray powder diffraction (XRD), Fourier transfer infrared (FTIR) spectroscopy and scanning electron microscope (SEM). Thermal behavior and the morphology of the synthesized Ca(H₂PO₄)₂·H₂O in aqueous and acetone media are compared with those of other works. The SEM micrograph of Ca(H₂PO₄)₂·H₂O show parallelogram-like microparticles containing small and large grain sizes. The aqueous and acetone media are proposed to play an important role in the synthetic process of calcium phosphates in exhibiting different physical properties, which are important for specific applications.     

Synthesis and crystal structure of a new calcium borate, CaB6O10

A new calcium borate, CaB₆O₁₀, has been prepared by solid-state reactions at temperature below 750 °C. The single-crystal X-ray structural analysis showed that CaB₆O₁₀ crystallizes in the monoclinic space group P2₁/c with a = 9.799(1) Å, b = 8.705(1) Å, c = 9.067(1) Å, β = 116.65(1)°, Z = 4. It represents a new structure type in which two [B₃O₇]⁵⁻ triborate groups are bridged by one oxygen atom to form a [B₆O₁₃]⁸⁻ group that is further condensed into a 3D network, with the shorthand notation 6: ∞³[2 × (3:2Δ + T)]. The 3D network affords intersecting open channels running parallel to three crystallographically axis directions, where Ca²⁺ cations reside. The IR spectrum further confirms the presence of both BO₃ and BO₄ groups.     

Low-temperature fabrication of high purity Ti3SiC2

In this study, we fabricated high purity Ti₃SiC₂ ceramic by mechanical alloying (MA) and spark plasma sintering (SPS), and investigated the effect of trace amount of Al on these processes. Our results show that addition of proper amount of Al significantly increases the purity of Ti₃SiC₂ in the MA and subsequent SPS products, and remarkably reduces the sintering temperature for Ti₃SiC₂. Ti₃SiC₂ sintered compact with a purity of 96.5 wt% was obtained by 10 h of MA and subsequent SPS from a starting mixture composed of n(Ti):n(Si):n(Al):n(c) = 3:1:0.2:2 at 850 °C. At 1100 °C, Ti₃SiC₂ with a purity of 99.3 wt% and a relative density of 98.9% was obtained.     

Thermodynamic study of CVD–ZrO2 phase diagrams

Chemical vapor deposition (CVD) of zirconium oxide (ZrO₂) from zirconium acetylacetonate Zr(acac)₄ has been thermodynamically investigated using the Gibbs’ free energy minimization method and the FACTSAGE program. Thermodynamic data Cp°, ΔH° and S° for Zr(acac)₄ have been estimated using the Meghreblian–Crawford–Parr and Benson methods because they are not available in the literature. The effect of deposition parameters, such as temperature and pressure, on the extension of the region where pure ZrO₂ can be deposited was analyzed. The results are presented as calculated CVD stability diagrams. The phase diagrams showed two zones, one of them corresponds to pure monoclinic phase of ZrO₂ and the other one corresponds to a mix of monoclinic phase of ZrO₂ and graphite carbon.     

Structures, electrical and thermal expansion properties of Sr-doped La2Mo2O9 oxide-ion conductors

The oxide-ion conductors (La_1−xSr_x)₂Mo₂O_9−δ (x = 0.01–0.08) were prepared by means of a conventional solid-state reaction. The effects of Sr doping for La site on the structures, electrical and thermal expansion properties of the oxide-ion conductor La₂Mo₂O₉ were investigated using X-ray diffraction, direct current four-probe method, thermal dilatometer and scanning electron microscopy, respectively. The results show that the lattice constants were first decreased, then increased, and decreased again with the increase of Sr doping content. The solid solubility of Sr in (La_1−xSr_x)₂Mo₂O_9−δ is x = 0.07. The sinterability of samples is markedly improved with the increase of Sr doping content. The sintered density of sample x > 0.07 is higher than 96% of its theoretical density. When x > 0.02, doping Sr in La₂Mo₂O₉ can inhibit the excessive growth of grains, thus increases the sintered density of samples. The structural transition temperature shifts to the low side with the increase of Sr doping content, and the phase transition is completely suppressed when the doping content reaches 0.07. The conductivity of sample increases with the increase of Sr doping content. The conductivity of sample x = 0.07 reaches a maximum of 0.078 S/cm and 0.101 S/cm at 800 °C and 850 °C, respectively. In this study, it was demonstrated that doping 7 mol% Sr for La site not only can completely suppress the structural phase transition in La₂Mo₂O₉, but also can effectively enhance electrical conductivity of samples at higher temperature.     

Thermodynamic studies on LaFeO3(s)

The enthalpy increments and the standard molar Gibbs energies in the formation of LaFeO₃(s) have been measured using a high-temperature Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. The corresponding expression for enthalpy increments is given as:

H°(T)−H°(298.15 K)(J mol⁻¹)(±1.2%)=−36887.27+103.53 T(K)+25.997×10⁻³T²(K)+11.055×10⁵/T(K).

The heat capacity, the first differential of H°(T)−H°(298.15 K) with respect to temperature, is given as:

C_p,m°(T)(JK⁻¹mol⁻¹)=103.53+51.994×10⁻³T(K)−11.055×10⁵/T²(K).

From the measured e.m.f. of the cell, (−)Pt/(LaFeO₃(s)+La₂O₃(s)+Fe(s))//CSZ//(Ni(s)+NiO(s))/Pt(+), and the relevant Δ_fG_m°(T) values from the literature, the Δ_fG_m°(LaFeO₃, s, T) was calculated, and is given as:

Δ_fG_m°(LaFeO₃, s, T)(kJmol⁻¹)(±0.72)=−1319.2+0.2317T(K).

The calculated Δ_fH_m°(LaFeO₃, s, 298.15 K) and S°(298.15 K) values obtained using the second law method are −1334.7 kJ mol⁻¹ and 128.9 J K⁻¹ mol⁻¹, respectively.     

Effect of CrB2 addition on densification, properties and oxidation resistance of TiB2

This paper presents the results of detailed studies carried out on the densification of TiB₂ with CrB₂ as sinter additive by hot pressing. The dense compacts were characterized by measurement of hardness, indentation fracture toughness, flexural strength, coefficient of thermal expansion and electrical resistivity. Oxidation characteristics were investigated between 600 °C and 1000 °C and isothermal oxidation kinetics at 850 °C. Phase identification and surface morphology analysis of hot pressed and oxidized samples were done using XRD and SEM. A high density of 96.61% Τ.D was obtained with the addition of 2.5% CrB₂ by hot pressing at 1750 °C under 35 MPa pressure. Hardness values of composites with 2.5–10% CrB₂ were close to 24 GPa and fracture toughness in the range of 3–5 MPa m^1/2. Coefficient of thermal expansion of the composite with 10% CrB₂ was measured in the range of 6.21–7.43 × 10⁻⁶/K from room temperature to 1000 °C. Electrical resistivity of TiB₂ + 10%CrB₂ was measured as 32.83, 75.97 and 120 μΩ cm at 25 °C, 500 °C and 900 °C, respectively. Observed nature of oxidation was parabolic for all composites. Formation of continuous and thick glassy film was observed with increased CrB₂ content in the composite. TiO₂ and CrBO₃ phases were identified on the oxidized surface which are responsible for the improved oxidation resistance of this composite.     

Thermo-physical and thermal cycling properties of plasma-sprayed BaLa2Ti3O10 coating as potential thermal barrier materials

Increased turbine inlet temperature in advanced turbines has promoted the development of thermal barrier coating (TBC) materials with high-temperature capability. In this paper, BaLa₂Ti₃O₁₀ (BLT) was produced by solid-state reaction of BaCO₃, TiO₂ and La₂O₃ at 1500 °C for 48 h. BLT showed phase stability between room temperature and 1400 °C. BLT revealed a linearly increasing thermal expansion coefficient with increasing temperature up to 1200 °C and the coefficients of thermal expansion (CTEs) are in the range of 1 × 10^− 5–12.5 × 10^− 6 K^− 1, which are comparable to those of 7YSZ. BLT coatings with stoichiometric composition were produced by atmospheric plasma spraying. The coating contained segmentation cracks and had a porosity of around 13%. The microhardness for the BLT coating is 3.9–4.5 GPa. The thermo-physical properties of the sprayed coating were investigated. The thermal conductivity at 1200 °C is about 0.7 W/mK, exhibiting a very promising potential in improving the thermal insulation property of TBC. Thermal cycling result showed that the BLT TBC had a lifetime of more than 1100 cycles of about 200 h at 1100 °C. The failure of the coating occurred by cracking at the thermally grown oxide (TGO) layer due to severe oxidation of bond coat. Based on the above merits, BLT could be considered as a promising material for TBC applications.