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.     

Synthesis and photoluminescence of Sb-induced ZnO nanowires along with islands attached

ZnO nanowires with nanoislands attached are synthesized by thermal evaporation process using Sb as dopant. The electron microscopy and energy-dispersive X-ray spectroscopy show that the nanowires grow along with as side surfaces. The nanoislands are composed of SiO_x shelled ZnO clusters and attached to polar surface . We believe that the Sb dopant induces the growth along the distinct direction and leads the formation of additional structures on ZnO nanowires’ polar surface. The temperature-dependent photoluminescence confirms the existence of acceptor level related to Sb.     

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.     

Optical constants of TiO1.7 thin films deposited by electron beam gun

Electron beam evaporation technique was used to prepare TiO_1.7 thin films onto glass substrates of thicknesses 50, 500 and 1000 nm for each sample. Transmittance measurements in the wavelength range (350–2000 nm) were used to calculate the refractive index n and the absorption index k using Swanepole's method. The optical band gap determined by three different methods and the values obtained were in the same harmony. Optical conductivity σ_opt, complex dielectric constant, relaxation time τ and dissipation factor tan δ were determined. The analysis of the optical absorption data indicates that the optical band gap was indirect transitions. According to Wemple and Didomenico method, the optical dispersion parameters E_o and E_d were determined.     

Al-rich region of Al–Pd–Ru at 1000 to 1100 °C

Partial isothermal sections of the Al–Pd–Ru phase diagram at 1000, 1050 and 1100 °C are presented here. The Al–Pd orthorhombic -phases dissolve up to 15.5 at.% Ru, Al₁₃Ru₄ <2.5 at.% Pd and Al₂Ru up to 1 at.% Pd. Between 66 and 75 at.% Al, ternary quasiperiodic icosahedral phase and three cubic phases: C (, a = 0.7757 nm), C₁ (, a = 1.5532 nm) and C₂ (, a = 1.5566 nm) were revealed. An additional complex cubic structure with a ≈ 3.96 nm was found to be formed at compositions close to those of the icosahedral phase.     

The isostructural phase transition and frustrated magnetic ordering in TbPd0.9Ni0.1Al studied by neutron diffraction

By using powder neutron diffraction we provide a detailed structural and magnetic investigation of the pseudo-ternary compound TbPd_0.9Ni_0.1Al with hexagonal ZrNiAl-type crystal structure and disorder of palladium and nickel atoms on two crystallographic sites. We provide experimental evidence for the occurrence of an isostructural phase transition in TbPd_0.9Ni_0.1Al at 157 K, which is affected by structural disorder compared to that observed in TbPdAl. In TbPd_0.9Ni_0.1Al the step of the c/a ratio at the first-order phase transition appears about four times smaller than in TbPdAl. TbPd_0.9Ni_0.1Al undergoes two successive magnetic phase transitions at T_N1=41 K and T_N2≈21.5 K. Two third of non-frustrated ordered Tb moments form commensurate antiferromagnetic chains () and coexist with one third of frustrated ordered Tb moments, which change from a commensurate structure () between T_N2 and T_N1 to an incommensurate structure () below T_N2. Due to the strong magneto-crystalline anisotropy all ordered Tb moments stay perpendicular to the ab-plane and reach at 1.5 K saturation values of 8.6 (2) μ_B (non-frustrated) and 7.2 (2) μ_B (frustrated). The symmetry of the magnetic structure of TbPd_0.9Ni_0.1Al is lower than that of TbNiAl.     

Formation of Fe(III)-containing mackinawite from hydroxysulphate green rust by sulphate reducing bacteria

The interactions between Fe(II–III) hydroxysulphate GR() and sulphate reducing bacteria (SRB) were studied. The considered SRB, Desulfovibrio desulfuricans subsp. aestuarii ATCC 29578, were added with GR() to culture media. Different conditions were envisioned, corresponding to various concentrations of bacteria, various sources of sulphate (dissolved  + GR() or GR() alone) and various atmospheres (N₂:H₂ or N₂:CO₂:H₂). In the first part of the study, CO₂ was deliberately omitted so as to avoid the formation of carbonated compounds, and GR() was the only source of sulphate. Cell concentration increases from 4 × 10⁷ to 7 × 10⁸ cells/mL in 2 weeks. The evolution with time of the iron compounds, monitored by Raman spectroscopy and X-ray diffraction, showed the progressive formation of a FeS compound, the Fe(III)-containing mackinawite. This result is consistent with the association GR()/SRB/FeS observed in rust layers formed on steel in seawater. In the presence of CO₂ and additional dissolved sulphate species, a rapid growth of the bacteria could be observed, leading to the total transformation of GR() into mackinawite, found in three physico-chemical states (nanocrystalline, crystalline stoichiometric FeS and Fe(III)-containing), and siderite FeCO₃.     

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.     

Subsolidus phase relationships in the system ZnO–Li2O–WO3

The subsolidus phase relationships of the system ZnO–Li₂O–WO₃ have been investigated by X-ray diffraction (XRD) analyses. There are one ternary compound, five binary compounds and eight 3-phase regions in this system. The new ternary compound Li₂Zn₂W₂O₉ was found by the powder diffraction pattern. The corresponding crystal structure of this compound was refined by Rietveld profile fitting method. It belongs to a trigonal system with space group and lattice constants are a = 5.1438(2) Å, c = 14.1052(3) Å, and its thermal property was studied.     

FT-Raman and FT-IR vibrational spectroscopic studies of nanocrystalline Ba2RESbO6 (RE = Sm, Gd, Dy and Y) perovskites

The nanoparticles of Ba₂RESbO₆ (RE = Sm, Gd, Dy and Y) were synthesized using auto ignition combustion process. The structure and phase purity of the as-prepared nanopowders were examined by X-ray diffraction pattern. A systematic analysis of the structure of the four compounds was carried out for the first time by recording Raman and IR spectra. The four Raman active modes A_1g, E_g and 2F_2g were observed as strong or medium intense bands in the Raman spectra and the IR active F_1u(1) mode is obtained as a strong absorption band around 630 cm⁻¹ in all the four compounds. Hence it is confirmed that the above compounds were crystallized in the cubic symmetry with space group.     

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.     

Surface characteristics of micro-ultrasonically machined (1 0 0) silicon

Micro-ultrasonic machining of single crystal silicon was performed using 0.1 and diamond abrasives and a diameter cemented carbide cylindrical tool. The depth of cut was varied from 200 to 1400 nm and the average surface roughness was found to be 5–15 nm Sa. Confocal Raman microscopy of the cut surface indicated the presence of both diamond cubic and amorphous phases of silicon.     

Synthesis and characterization of framework-substituted Cs8Na16Cu5Ge131

We report the synthesis and temperature-dependent transport properties of a new type II germanium clathrate, Cs₈Na₁₆Cu₅Ge₁₃₁ (space group ; a = 15.42000(9) Å). In comparison to the parent compound Cs₈Na₁₆Ge₁₃₆, Cu substitution for Ge on the clathrate framework was found to increase in magnitude the electrical resistivity and Seebeck coefficient, while reducing the thermal conductivity. The results are consistent with partial charge compensation due to Cu substitution for Ge. In addition to presenting possibilities for new compositions, framework substitution in type II clathrates may offer a route to control the transport properties of these materials, and could offer potential candidates for thermoelectric applications.     

Preparation of a 16-hydroxyhexadecanoate ion self-assembled monolayer on a zinc electrode coated with hydrated cerium(III) oxide

A self-assembled monolayer (SAM) of 16-hydroxyhexadecanoate ion was prepared on a zinc electrode coated with a hydrated cerium(III) oxide Ce₂O₃ layer. The protective efficiency, P of the duplex film composed of the Ce₂O₃ layer and the SAM was examined by polarization measurement of the zinc electrode in aerated 0.5 M NaCl. The P value of the HOC₁₆A⁻ SAM on the Ce₂O₃-coated electrode was only a little higher than that of the Ce₂O₃-coated one. The contact angle of the surface covered with the film with a drop of water was far higher than the value of the HOC₁₆A⁻ SAM on passivated iron, suggesting that HOC₁₆A⁻ was partly adsorbed on the Ce₂O₃ surface via both and OH groups in a looped orientation. Because this orientation must be changed to an extended orientation during immersion in 0.5 M NaCl, some defects appeared within the SAM in places, resulting in a poor enhancement of P. The film structure was characterized by X-ray photoelectron and FTIR reflection spectroscopies.     

Zinc-deficiency in intermetallics with the NaZn13 type: Re-determination of the crystal structure and physical properties of EuZn13−x (x = 0.25(1))

Reported are the synthesis from zinc flux, crystal structure re-determination from single-crystal X-ray diffraction, and magnetic properties of EuZn_13−x (x = 0.25(1)). It crystallizes in the cubic NaZn₁₃ type (Pearson's symbol cF112, space group , No. 226) with unit cell parameter a = 12.1651(17) Å, determined at 120 K. The structure has two crystallographically unique zinc sites, one of which is partially occupied. This finding is consistent with previous experimental and theoretical work on related Zn-rich networks that suggests an optimal electron count of 27 electrons per formula unit. Temperature-dependent magnetization measurements confirm that the Eu ions in EuZn_12.75(1) are divalent as evidenced from the effective magnetic moment of 7.98μ_B.     

Characteristics of thermal transitions during annealing of a nanocrystalline Ni3Al-based alloy

In this study, the changes in atomic ordering of a Ni₃Al-based alloy were investigated. The mechanically alloyed powders were annealed at different temperatures up to 1300 °C and then subjected to X-ray diffraction (XRD) analysis. In addition, differential thermal analysis (DTA) with different heating rates was used for calculating the activation energy (using Kissinger and Augis & Bennet methods) and enthalpy of the three transitions: atomic ordering of crystalline structure, transformation of and melting. According to the results obtained, the maximum atomic ordering in this Ni₃Al-based alloy obtained at 600 °C, beyond which it decreased with increasing temperature. Ultimately, atomic ordering completely vanished at 1300 °C due to a lattice transformation occurring from L1₂ ordered structure to the Ni-based solid solution phase.     

Determination of the structure of a new tetragonal U2FeAl20 phase

The atomic structure of a new ternary U₂FeAl₂₀ phase appearing in the Al-rich corner of a U–Fe–Al system was solved using electron crystallography and X-ray powder diffraction techniques (XRD). The positions of U atoms were determined from crystallographically processed high-resolution electron microscopy (HRTEM) images. These positions were used as a starting set for determining the coordinates of Fe and Al atoms by difference-Fourier synthesis technique. The U₂FeAl₂₀ phase is tetragonal and belongs to the space group. Its unit cell contains 80 Al, 4 Fe, and 8 U atoms. The lattice parameters obtained after Rietveld refinement are: a = 12.4138 Å, c = 10.3014 Å. The reliability factors characterizing the Rietveld refinement procedure are: R_p = 8.65%, R_wp = 11.2% and R_b = 5.93%.     

The Ag–Cu–Ge ternary phase diagram

The Ag–Cu–Ge phase diagram is not very well elaborated. In this work an attempt is made to validate the phase diagram in the area of the ternary eutectic and to decide whether it is a suitable model system for solidification experiments. The different steps in the solidification sequence are separately discussed and analysed. It is shown that an optimization of the system is necessary. The experiments in this work demonstrate that the transition reaction Ge is located closer to the ternary eutectic than assumed in earlier work.     

Influence of sintering temperature and oxygen stoichiometry on electrical transport properties of La0.67Na0.33MnO3 manganite

With a view to investigate the influence of sintering temperature and oxygen stoichiometry on electrical and magnetic properties of sodium-doped lanthanum manganite sintered at different temperatures, a series of samples were prepared by the sol–gel route. The samples were characterized by the XRD studies and the data were analyzed using the Rietveld refinement technique and it has been observed that the materials are having rhombohedral structure with space group. The electrical resistivity and thermoelectric power studies were investigated both as a function of crystallite size and oxygen content. To understand the conduction mechanism, the electrical resistivity data have been analyzed and it has been concluded that the variation of electrical resistivity in the ferromagnetic region can be explained by electron–electron scattering process (T²) and two magnon scattering processes, while that in the paramagnetic region is explained by the small polaron hopping mechanism. Similarly, the variation of thermopower in the ferromagnetic region is explained on the basis of electron–magnon scattering.     

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.