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.     

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.     

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.     

Sn Mössbauer spectroscopy of the intermetallic compound HoRhSn

The powder X-ray diffraction data revealed that the structure of HoRhSn is isotypic with the hexagonal ZrNiAl type (space group ). Bulk magnetic AC and DC measurements have shown that this compound is ferromagnetic with a Curie temperature of T_C = 6.3(2) K. The thermal variation of the hyperfine parameters has been studied in detail by ¹¹⁹Sn Mössbauer spectroscopy. Especially, large distribution of magnetic hyperfine fields observed at the tin sites points to a rather complicated magnetic structure of probably non-collinear character but with the magnetic holmium moments arranged in directions close to the c-axis.     

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.     

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.     

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.     

Crystal structure, thermal expansion and electrical properties of the new Al0.32ErGe2 compound

A new ternary compound Al_0.32ErGe₂ has been synthesized and studied from 298 K to 773 K using X-ray powder diffraction technique. Its structure has been determined at room temperature by Rietveld refinement of X-ray powder diffraction data. The ternary compound Al_0.32ErGe₂ crystallizes in the orthorhombic with the defect CeNiSi₂ structure type (space group Cmcm, a = 0.40701(2) nm, b = 1.60401(9) nm, c = 0.39240(2) nm, Z = 4 and D_calc = 8.326 g/cm³). The average thermal expansion coefficients , and of Al_0.32ErGe₂ are 1.72 × 10⁻⁵ K⁻¹, 1.11 × 10⁻⁵ K⁻¹ and 1.52 × 10⁻⁵ K⁻¹, respectively. The bulk thermal expansion coefficient is 4.35 × 10⁻⁵ K⁻¹. Electrical resistivity of Al_0.32ErGe₂ was measured between 5 K and 300 K.     

Investigation of DC conductivity and switching phenomenon of Se80Te20−xGex amorphous system

Se₈₀Te_20−xGe_x (x = 5, 7 and 10 at%) chalcogenide glass system was prepared by the conventional melt-quenching technique. Thin films of different thicknesses (283–823 nm) were prepared by thermal evaporation technique. The DC conductivity and switching properties were investigated in the temperature range 303–373 K below the corresponding glass transition temperature. The obtained results of DC conductivity showed that it decreases with decreasing Te content in the considered system, while it increases with temperature as well as with film thickness through the studied range. The conduction activation energy has two values E_σ1 and E_σ2 indicating the presence of two different conduction mechanisms through the studied range of temperature. The obtained results of the temperature dependence of DC conductivity are explained in accordance with Mott and Davis model. The switching effect in amorphous films was also investigated. The switching phenomenon for these compositions was of the memory type. The mean value of the threshold voltage increases linearly with increasing film thickness in the range 283–823 mm, while it decreases exponentially with increasing temperature in the investigated range. Values of the threshold voltage and power activation energies were obtained for the investigated compositions. The obtained results agree with the electrothermal model for the switching process.     

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.     

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.     

Determination of the crystal structure of the phase in the Fe–Al system by high-temperature neutron diffraction

The crystal structure of the high-temperature phase of the Fe–Al system has been determined by in-situ high-temperature neutron diffraction for the first time and the crystallographic parameters have been established by Rietveld refinement of the data. The phase was found to have a body-centered cubic structure of the Hume-Rothery Cu₅Zn₈-type (space group I3m (No. 217), Z = 4, Pearson symbol cI52, Strukturbericht designation D8₂). Accordingly, the ε phase has the formula Fe₅Al₈. Its lattice parameter is a = 8.9757(2) Å at 1120 °C, which is 3.02 times that of cubic FeAl (B2) at the same temperature. All fractional atomic coordinates, site occupation factors and interatomic distances were determined and it was examined how this phase can meet the rules for Hume-Rothery-type phases.     

Effect of potassium doping on the structural, magnetic and magnetocaloric properties of La0.7Sr0.3−xKxMnO3 perovskite manganites

We investigate the effect of potassium doping on the structural, magnetic and magnetocaloric properties of La_0.7Sr_0.3−xK_xMnO₃ (x = 0.05, 0.1, 0.15 and 0.2) powder samples. Our polycrystalline compounds were synthesized using the solid-state reaction at high temperature. X-ray diffraction characterizations showed that all our studied samples crystallize in the distorted rhombohedral system with space group. With increasing potassium content, the unit cell volume exhibits a broad maximum around x = 0.15. Magnetization measurements versus temperature showed that all our samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature T_C is found to decrease from 365 K for x = 0 to 328 K for x = 0.2 as well as the saturated magnetization M_sp which shifts from 3.68 μ_B/Mn for x = 0 to 3.05 μ_B/Mn for x = 0.2. The critical exponent γ defined as M_sp (T) = M_sp(0)[1−(T/T_C)]^γ is found to remain almost constant and equal to 0.33 for all our samples. The maximum of magnetic entropy changes |ΔS_max| of La_0.7Sr_0.3−xK_xMnO₃ for x = 0.05 and 0.15 is found to be respectively, 1.37 and 1.2 J kg⁻¹ K⁻¹ under a magnetic field change of 1 T.     

Synthesis and properties of CaCd2Sb2 and EuCd2Sb2

High density polycrystalline CaCd₂Sb₂ and EuCd₂Sb₂ intermetallics are synthesized by Spark Plasma Sintering and their thermoelectric properties are investigated. X-ray diffraction measurements reveal both materials have a structure in space group, containing a small amount of CdSb as a second phase. Thermoelectric measurements indicate both are p-type conductive materials. The figure of merit value of CaCd₂Sb₂ is 0.04 at 600 K and that of EuCd₂Sb₂ is 0.60 at 617 K. Theoretical calculations show that CaCd₂Sb₂ is a degenerate semiconductor with a band gap of 0.63 eV, while EuCd₂Sb₂ is metallic with DOS of 13.02 electrons/eV. For deeper understanding of the better thermoelectric properties of EuCd₂Sb₂, its low temperature magnetic, transport and heat capacity properties are investigated. Its Nèel temperature is 7.22 K, convinced by heat capacity anomaly at 7.13 K. Hall effect convinced that it is a p-type conductive material. It has high Hall coefficient, high carrier concentration and high carrier mobility of +1.426 cm³/C, 4.38 × 10¹⁸/cm³ and 182.40 cm²/Vs, respectively. They are all in the magnitude of good thermoelectric materials. The Eu 4f level around Fermi energy and antiferromagnetic order may count for the better thermoelectric properties of EuCd₂Sb₂ than that of CaCd₂Sb₂.     

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.     

Magnetic phase diagram of CrTe1−xSbx (0.0≤x≤1.0)

Measurements of the high field magnetization of CrTe_1−xSb_x (0.0≤x≤1.0) were carried out at 4.2 K in pulsed magnetic fields up to 300 kOe. The temperature dependence of the magnetization of CrTe_1−xSb_x was measured in the temperature range from 4.2 K to 800 K. The magnetic phase diagram of CrTe_1−xSb_x (0.0≤x≤1.0) was determined, which is similar to the typical one for the mixed crystals of the layered antiferromagnetic and ferromagnetic compounds proposed by de Gennes.     

Structural, magnetic and electrical transport properties for a series of La1−xSrxFe1−xMnxO3 (0.3 ≤ x ≤ 0.7) compounds

The structural, electrical transport and magnetic properties have been studied for compounds: La_1−xSr_xFe_1−xMn_xO₃ (0.3 ≤ x ≤ 0.7). The lattice parameter, a, first decreases with x, and followed by an increase when Sr²⁺ and Mn⁴⁺ was continuously doped. The cell parameters, b and c, slightly decrease with coupled substitution of Sr²⁺ for La³⁺ and Mn⁴⁺ for Fe³⁺. In the paramagnetic temperature range, formation of magnetic clusters is suggested; the sizes of clusters decrease with x up to 0.5, following that they increase sharply with continuing doping. The electrical behaviors of all specimens demonstrate insulators and the electrical resistivity increases with content of Mn⁴⁺ and Sr²⁺ ions doped. A variable range hopping model is suitable to describe electrical transport process for the compounds at low temperature. At high temperature the electrical transport process can be described by bipolaron model for all compounds.     

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.     

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.