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.     

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.     

Crystal structure and microwave dielectric properties of a new A4B3O12-type cation-deficient perovskite Ba3LaTa3O12

A new microwave dielectric ceramic Ba₃LaTa₃O₁₂ has been prepared by conventional solid-state ceramic route. Through Rietveld refinement of X-ray powder diffraction data, the compound is identified as an A₄B₃O₁₂-type B-site cation-deficient perovskite with space group and lattice constants a = 5.7573(2) Å, c = 28.2386(2) Å, V = 810.62(4) Å³ and Z = 3. The microwave dielectric properties of Ba₃LaTa₃O₁₂ were investigated. The compound exhibits a relative dielectric constant (_r) of 36.8, a quality factor Q_u × f of 21,965 at 6.4040 GHz and a small negative temperature coefficient of resonant frequency (τ_f) of −49.6 ppm/°C.     

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.     

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.     

Structural investigation of the phase transitions of Tribromo ammonium mercurate (II) monohydrate, NH4HgBr3·H2O

Single crystal diffraction, Infrared spectroscopy and differential scanning calorimetry DSC techniques have been used to investigate the different phases of NH₄HgBr₃·H₂O, Tribromo ammonium mercurate (II) monohydrate, from room temperature to 120 K. Two anomalies in thermal behaviour were detected for this compound at 198 and 340 K, by DSC experiment. X-ray diffraction measurements confirm the presence of the first anomaly. At room temperature NH₄HgBr₃·H₂O, crystallizes in the orthorhombic space group Cmc2₁, with the lattice constants a = 4.475(1) Å, b = 17.226(2) Å, c = 10.240(2) Å and Z = 4. Below 200 K the structure is monoclinic P2₁ with: a = 4.379(4) Å, b = 17.220(10) Å, c = 10.103(2) Å, β = 90.023(9)° and Z = 2 (T = 120 K). The mercury atom is surrounded by four bromine atoms in an irregular tetrahedron. The tetrahedra are linked at two corners, resulting in infinite chains along the “a” axis. The ammonium groups are located between the chains ensuring the stability of the structure by hydrogen bonding contacts: NHBr, OHBr, NHO. The structural phase transformation was attributed to an orientational disorder of ammonium groups.     

A convenient thermal reduction–nitridation route to nanocrystalline molybdenum nitride (Mo2N)

Nanocrystalline molybdenum nitride (γ-Mo₂N) was synthesized via a thermal reduction–nitridation route by the reaction of metallic sodium with anhydrous molybdenum pentachloride and ammonium chloride in an autoclave at 550 °C. X-ray powder diffraction pattern indicated that the product was cubic Mo₂N, and the cell constant was a = 4.161 Å. Scanning electron microscopy image showed that it consisted of particles with an average size of about 30 nm. The product was also studied by BET and TGA. It had good thermal stability and oxidation resistance below 400 °C in air.     

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.     

Synthesis and characterization of new pyrochlore solid solution Bi1.5Sb1.5Cu1−xMnxO7

A new pyrochlore solid solution with formula Bi_1.5Sb_1.5Cu_1−xMn_xO₇ has been synthesized using ceramic method at 1000 °C. The cell parameter decreases linearly with increasing manganese concentration. Rietveld refinements for (B_1.5Mn_0.5)(Sb_1.5Mn_0.5)O₇ compound using X-ray powder diffraction data confirmed an overall A₂B₂O₇ cubic pyrochlore structure with a = 10.42749 (4) Å and Fd-3m symmetry. The reliability factors are R_wp = 3.48%; R_p = 2.37%; R_exp = 1.65% and R_Bragg = 1.58%. The magnetic susceptibility measurements achieved between 4 and 300 K indicate a paramagnetic behaviour with an oxidation state “2+” of the manganese ion. The electric resistance measured using complex impedance spectroscopy method put in evidence a decrease of the electric resistance with the temperature, which reached 5 × 10² Ω at 675 K. Dielectric properties depend on the variation of frequency and temperature, results indicate a conductive compound.     

Synthesis, characterization and magnetic properties of complex oxides Ln2Mn2/3Re4/3O7 (Ln = Er, Y) and Y2Zn2/3Re4/3O7

Complex oxides Ln₂Mn_2/3Re_4/3O₇ (Ln = Y, Er) and Y₂Zn_2/3Re_4/3O₇ with a zirkelite structure and hexagonal unit cells (space group P3₁21, z = 6) have been obtained. Static and dynamic magnetic susceptibility measurements show that these oxides possess spin-glass behavior at low temperatures. Valence combinations of d-metals in the oxides are Mn²⁺(Zn²⁺)–Re⁵⁺. It is supposed that the examined specimens Ln₂Mn_2/3Re_4/3O₇ (Ln = Y, Er) contain the second magnetic phase of an unknown composition.     

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.     

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.     

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.     

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.     

Subsolidus phase relations in the system ZnO–P2O5–MoO3

The subsolidus phase relations of the ternary system ZnO–P₂O₅–MoO₃ were investigated by means of X-ray diffraction (XRD). Seven binary compounds and eight 3-phase regions were determined, and no ternary compound was found in this system. The phase diagram of pseudo-binary system Zn₃(PO₄)₂–Zn₃Mo₂O₉ was also constructed through XRD and differential thermal analysis (DTA) methods, and the result reveals this system is eutectic system. The eutectic temperature is 904 °C and the corresponding component is 30% Zn₃Mo₂O₉ and 70% Zn₃(PO₄)₂.     

Preparation and photocatalytic activity of nano-sized nickel molybdate (NiMoO4) doped bismuth titanate (Bi2Ti4O11) (NMBT) composite

Various compositions of nano-sized (NiMoO₄)_x-doped Bi₂Ti₄O₁₁ (x = 0.01, 0.05, 0.1) composites have been prepared by chemical solution decomposition (CSD) method using triethanolamine (TEA) as complexing agent. Ni(II) is one of reactive species on the catalyst surface and Mo(VI) ion helps to compensate the charge of the lattice. The photocatalysts based on the above compositions have been tested for photobleaching of methyl orange (MO) solution under Hg-lamp. The prepared nanopowders are characterized by XRD, EDAX, UV–vis spectra, specific surface area (BET), zeta potential, ESR and HRTEM analyses. The average particle size of nickel molybdate-doped bismuth titanate lies around 30 ± 2 nm measured from TEM. Result shows nickel molybdate-doped bismuth titanate (NiMoO₄)_x(Bi₂Ti₄O₁₁)_1−x (NM_xBT_1−x; x = 0.01) composite is found to be more photoactive compared all the compositions studied except degussa P25 titania.     

The crystal structure of LiMgAlD6 from combined neutron and synchrotron X-ray powder diffraction

LiMgAlH₆ is the intermediate phase when LiMg(AlH₄)₃ is heated. It contains 9.4 wt.% hydrogen, of which 4.8 wt.% is released during the decomposition step to MgH₂ and LiH. Deuterated LiMgAlD₆ was prepared by heat-treating LiMg(AlD₄)₃ at 130 °C. Powder neutron and synchrotron X-ray diffraction patterns were measured and the structure was refined using the Rietveld technique on both patterns simultaneously. LiMgAlD₆ crystallizes in the trigonal space group P321 with a = 7.9856(4) Å and c = 4.3789(3) Å. The structure consists of isolated AlD₆ octahedra connected through octahedrally coordinated Mg- and Li-atoms.     

LiSrGe2 and LiBaGe2: One-dimensional chains of in an unusual conformation

Two new isostructural intermetallic germanides, LiSrGe₂ and LiBaGe₂, were synthesized as single crystals from constituent elements in molten Na. They both crystallize in the space group Pnma (no. 62) with a = 7.142(1), b = 4.459(1), c = 11.550(2) Å, Z = 4, and a = 7.381(1), b = 4.617(1), c = 11.837(1) Å, Z = 4, for LiSrGe₂ and LiBaGe₂, respectively. They contain one-dimensional anionic germanide chains, , running along the a-axis. The chains are in an unusual zigzag-like conformation, with weakly alternating Ge–Ge bond lengths of 2.475(1) and 2.498(1) Å, and 2.473(1) and 2.525(1) Å, for LiSrGe₂ and LiBaGe₂, respectively. Extended Hückel calculations suggest that LiSrGe₂ is metallic: the Fermi level lies within bands having anti-bonding character.     

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.     

Role of thermal stability and vapor pressure of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)magnesium(II) and its triamine adduct in producing magnesium oxide thin film using a plasma-assisted LICVD process

Thin films of magnesia were deposited on various substrates using plasma-assisted liquid injection chemical vapor deposition with volatile Mg(tmhd)₂·2H₂O (1) (tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione). The precursor complexes, Mg₂(tmhd)₄·(2), and Mg(tmhd)₂·pmdien (3) (pmdien; N,N,N′,N″,N″-pentamethyldiethylenetriamine) were prepared from Mg(tmhd)₂·2H₂O (1). The temperature dependence equilibrium vapor pressure (p_e)_T data yielded a straight line when log p_e was plotted against reciprocal temperature in the range of 360–475 K, leading to standard enthalpy of vaporization (Δ_vapH°) values of 59 ± 1 and 67 ± 2 kJ mol^− 1 for (2) and (3) respectively. Thin films of magnesium oxide were grown at 773 K using complex (1) on various substrate materials. These films were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray for their composition and morphology.