Crystal structures of the compounds formed in DyCo2–DyGa2 pseudo-binary system at 773 K

DyCo_2?xGa_x alloys with x from 0 to 2 were prepared by arc melting and investigated by X-ray powder diffraction. Six ternary compounds with different Ga contents x, DyCo₂, DyCo_1.33Ga_0.67, DyCoGa, DyCo_0.67–0.35Ga_1.33–1.65, DyCo_0.25–0.15Ga_1.75–1.85, and DyGa₂, were formed in the system. The crystal structures of these compounds were determined by Rietveld refinement method with TOPAS V3.0 software. The Rietveld refinements reveal that DyCo_1.33Ga_0.67 crystallized in the MgZn₂-type structure (P6₃/mmc) with a = 5.414(1) and c = 8.452(1) Å, DyCoGa in the Co₂Si-type structure (Pnma) with a = 7.052(1), b = 4.393(1) and c = 6.958(1) Å, DyCo_0.5Ga_1.5 in the GdPdSi-type structure (Imma) with a = 4.341(1), b = 7.007(1) and c = 7.551(1) Å, and DyCo_0.2Ga_1.8 in the AlB₂-type structure (P6/mmm) with a = 4.339(1) and c = 3.634(1) Å. The relationships between these structures were discussed.     

Magnetic and magnetocaloric properties of (MnCo)1 − x Ge compounds

The crystal structure, magnetic properties, and heat capacity of the (MnCo)_{1 ? x} Ge compounds with x ≤ 0.05 have been studied. It was found that, as the deviation from the MnCoGe stoichiometric composition increases, the temperature of structural transition from the low-temperature phase with the orthorhombic TiNiSi-type structure to the high-temperature phase with the hexagonal Ni₂In-type phase decreases rapidly, whereas the magnetic ordering temperature varies slightly. The temperature of structural transition for the composition with x = 0.02 approximately coincides with the Curie temperature of the hexagonal phase, and the transition is accompanied by a significant entropy change, namely, ΔS = 34 J/(kg K). The application of high magnetic field in the transition-temperature range causes an increase in the relative volume of the orthorhombic phase. An analysis of magnetocaloric properties of these compounds, which was performed with the formal application of the Maxwell’s relationship near the temperature of first-order structural phase transition, is shown to give overestimated values of the entropy change.     

Magnetic properties of the Mn1.9 − x Co x Ge compounds with a hexagonal crystal structure

Concentrational dependences of the lattice parameters, spontaneous magnetic moment, and magnetic ordering temperature of nonstoichiometric Mn_{1.9 ? x} Co _x Ge (0.8 < x < 1.65) compounds with a hexagonal crystal structure of the Ni₂In type have been studied. As the Co content (x) increases from 1.1 to 1.2, the Curie temperature and magnetic moment were found to increase abruptly. The magnetization curves measured for oriented single crystals indicate the presence of a concentrational spin-reorientation transition in this system. The experimental data obtained are discussed taking into account the results of energy-band electronic-structure calculations.     

Structural state of metastable cubic compounds Ni1 − x Zn x O (0.6 ≤ x ≤ 0.99)

The fine crystalline structure of metastable cubic oxide compounds Ni_{1 ? x} Zn _x O (0.6 ≤ x ≤ 0.99) has been examined using X-ray diffraction. The compounds have been synthesized from the original hexagonal phase by quenching specimens from an elevated temperature under an external hydrostatic pressure. It has been found that the diffraction patterns of the compounds include a system of superlattice diffuse maxima, the number and intensity of which depend greatly on their composition. The origin of this superstructure is discussed.     

Magnetocaloric effect of Pr2Fe17−x Mn x alloys

Polycrystalline Pr2Fe17-xMnx（x = 0, 1, and 2）alloys were studied by X-ray diffraction（XRD）, heat capacity, ac susceptibility, and isothermal magnetization measurements. All the alloys adopt the rhombohedral Th2Zn17-type structure. The Curie temperature increases from 283 K at x = 0 to 294 K at x = 1, and then decreases to 285 K at x = 2. The magnetic phase transition at the Curie temperature is a typical second-order paramagnetic–ferromagnetic transition. For an applied field change from0 to 5 T, the maximum-△SM for Pr2Fe17-xMnxalloys with x = 0, 1, and 2 are 5.66, 5.07, and 4.31 J·kg^-1·K^-1,respectively. The refrigerant capacity（RC） values range from 458 to 364 J·kg^-1, which is about 70 %–89 % that of Gd. The large, near room temperature △SM and RC values,chemical stability, and a high performance-to-cost ratio make Pr2Fe17-xMnxalloys be selectable materials for room temperature magnetic refrigeration applications.     

Effect of gallium on the crystal structure and magnetic properties of PrFe11 − x Ga x C y compounds

A homogeneity range of the PrFe_{11 ? x} Ga _x C _y phase was determined. As the gallium content increases, the lattice parameters were shown to increase, whereas the Curie temperature decreases; the type of magnetic anisotropy at room temperature is unchanged. In the alloys with x > 3, the transformation of the tetragonal lattice of the compound into an orthorhombic lattice with the axial ratio a/b ≤ 1.006 is observed. This is likely to be caused by the ability of gallium to form covalent bonds. Gallium atoms were found to occupy preferentially 16j ₂ and 4e ₂ sites in the orthorhombic lattice of the FePr_6.5Ga_4.5C compound. The atoms located in the 16j ₂ sites form wavy chains along the [010] direction of the orthorhombic lattice, whereas the iron atoms located in the 16j ₁ sites form analogous chains along the [100] direction. Owing to this fact, one of these directions is likely to become an easy axis. The alloy with x= 4.5 has a low coercive force at room temperature; at 114 K, its coercive force is H _c = 42.4 kA/m.     

Structure,magnetic properties,and thermal stability of Sm1−x Tm x Co5 compounds

Structure, magnetic properties, and thermal stability of ternary Sm1-xTmxCo5 compounds were studied via X-ray diffraction(XRD), thermal magnetic analysis(TMA), and magnetic measurements. XRD results show that all the compounds have a main phase of hexagonal CaCu5-type crystal structure with small amount of impurity phases; increasing Tm content is associated with contraction of the hexagonal unit cell in the direction of the c axis and expansion of the a and b parameters. TMA results indicate that the Curie temperature(TC) of Sm1-xTmxCo5 compounds gets higher with the increase in Tm content.Magnetic measurements show that both the magnetic anisotropy field(HA) and the magnetization at an applied field of 7 T(M7 T) decrease with the increase of Tm content. However, the thermal stability of both the HAand M7 Tof all the Tm doped compounds is remarkably improved compared with that of the pure SmCo5 compound, leading to the result that both the M7 Tand HAof Sm0.8Tm0.2Co5 .2are higher than those of SmCo5 compound at 473 K, which indicates the good potential of Tm doped compound in the practical applications at elevated temperature.     

Crystal structure and magnetic properties of pseudobinary solid solutions Pr(In1 − x Pb x )3

Structure and magnetic properties of Pr(In_{1 ? x} Pb _x )₃ alloys have been studied in some detail. It has been shown that, in this system, in the whole range of compositions (0 ≤ x ≤ 1), there is a continuous series of disordered solid solutions with a structure of the Cu₃Au type. The lattice parameter of these solid solutions varies linearly (according to Vegard’s law). The temperature dependence of the magnetic susceptibility has been studied in the temperature range of 2–300 K. At enhanced temperatures, it is described well by the Curie-Weiss law for all alloys. At low temperatures, an anomalous deviation from this law for the terminal alloys is observed, which is especially strong for PrIn₃. In pseudobinary alloys, this anomaly weakens and the magnetic susceptibility itself increases. In the concentration dependence of the susceptibility measured at 2 K, a maximum is observed. The specific features of the dependence of the magnetic susceptibility of pseudobinary alloys on the temperature and concentration x have been explained by a decrease in the local symmetry of crystal field at the sites of Pr³⁺ ions due to the partial random replacement of their nearest neighbors by atoms of different valences.     

Crystal structure and properties of the new ternary YbZnxGa4−x and Yb3Zn11−xGax phases

Crystal structures of three new ternary YbZn_xGa_4?x (0.25 ≤ x ≤ 0.5 and 0.75 ≤ x ≤ 2) and Yb₃Zn_11?xGa_x (3.5 ≤ x ≤ 4.2) phases have been determined by means of single crystal X-ray as well as powder diffraction. They crystallize in known structure types, namely: CaCu_0.15Ga_3.75, BaAl₄ and La₃Al₁₁. Magnetic and transport properties were investigated for the new YbZn_xGa_4?x compounds. All phases studied show metallic-like and diamagnetic behavior.     

Structure and magnetic properties of intermetallic compounds Gd5Si2-xGe2-xM2x

1 Introduction Nowadays, there is much interest in magnetic refrigeration materials, as they offer the prospect of an energy-efficient and environment friendly alternative for the traditional vapour cycle refrigeration technique. Magnetic refrigeration is…     

Crystal structures and thermal expansion properties of Y2-xErxMo4O15 （x=0.0-2.0） solid solutions

A new series of rare earth compounds,Y2-xErxMo4O15 （x=0.0-2.0）,were synthesized and their structures were determined by powder X-ray diffraction （XRD）. Rietveld analysis of XRD patterns reveals that the compounds of this series crystallize in monoclinic system with space group P21/c. The lattice parameters a,b,c,β and the unit cell volume V de-crease linearly with increasing Er content. The thermal expansion properties of these compounds were studied under high-temperature XRD. Positive thermal expansions of compounds Y2-xErxMo4O15 are found to be anisotropic along the three crystallographic directions where a and c axes expand while b axis contracts in the whole temperature range. By analysis of data,the expansion of weak band Mo2-O14 with rising temperature should be responsible for positive thermal expansion.     

Magnetoresistivity of Ce1−xLaxCu4Al compounds

The dependence of magnetoresistivity (MR) on the temperature and the magnetic field for Ce_1–xLa_xCu₄Al (0 ≤ x ≤ 0.6) compounds has been investigated. In the low temperature region, magnetoresistivity exhibits a negative magnetic field dependence due to the Kondo effect. Magnetoresistivity measurements on the Ce_1–xLa_xCu₄Al alloys are analyzed basing on the calculations by Schlottmann for the Bethe-ansatz in the frames of the Coqblin–Schrieffer model. The analysis yields the values of the Kondo temperature T_K and effective moment of the Kondo ion μ_K.     

Specific heat of Ce1−xLaxNiAl4 compounds

The temperature dependence of the specific heat C_p(T) for the solid solution Ce_1?xLa_xNiAl₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) has been studied. The effective magnetic moment values obtained across the series are in far agreement with the value of 2.54 μ_B/Ce that corresponds to a free Ce³⁺ ion. The specific heat has been analyzed considering the electronic, phonon and Schottky contributions. In comparison to CeNiAl₄, the substitution of Ce by La drastically reduces the values of the electronic specific heat coefficient γ. At low temperatures the γ value depends strongly on the temperature range used for the extrapolation and on the magnetic field. The scheme of the energy levels created by the splitting due to the crystal field (CEF) has been determined from the Schottky anomaly and is different for all compositions. The logarithmic dependence of the specific heat, C_p/T ∝ ?lnT, on temperature indicates on the possibility of the non-Fermi liquid behavior for Ce_0.8La_0.2NiAl₄ and Ce_0.6La_0.4NiAl₄.     

Magnetic properties and magnetocaloric effect of Nd(Mn1−xFex)2Ge2 compounds

Polycrystalline Nd(Mn_1?xFe_x)₂Ge₂ (0 ≤ x ≤ 1) compounds have been prepared by arc-melting. X-ray powder diffraction analysis shows that all samples crystallize in the ThCr₂Si₂-type structure with the space group I4/mmm. The substitution of Fe for Mn results in decreases of the lattice constants a, c and the unit-cell volume V. Magnetic properties and magnetocaloric effect of the compounds Nd(Mn_0.9Fe_0.1)₂Ge₂ and Nd(Mn_0.8Fe_0.2)₂Ge₂ have been studied by magnetic measurements. A spin reorientation transition at about 188 K is observed for Nd(Mn_0.9Fe_0.1)₂Ge₂. The Nd(Mn_0.8Fe_0.2)₂Ge₂ compound shows more complicated magnetic behavior, which is characterized by four magnetic ordering states below room temperature. The maximum values of the magnetic entropy change are 2.35 and 1.84 J kg^?1 K^?1 for x = 0.1 and 0.2, respectively, under the applied field changing from 0 to 5 T. The relative cooling powers of Nd(Mn_0.9Fe_0.1)₂Ge₂ and Nd(Mn_0.8Fe_0.2)₂Ge₂ are 145.9 and 133.8 J kg^?1 under an applied field change of 5 T.     

TEM analysis of Gd5(SixGel−x)4, where x=1/2

The material Gd₅(Si_xGe_l−x)4, with x=1/2 was investigated using transmission electron microscopy. The material possesses a complex crystallographic structure and undergoes a unique, reversible, transformation at low temperatures and an irreversible high temperature transformation. The high, room and low temperature microstructures of arc-melted and heat treated samples are reported. Direct observation of the transformation with a discussion on the mechanism of the reversible, low temperature, phase transformation is detailed.     

Optical and photocatalytic properties of nanoparticulate (TiO2)x(ZnO)1−x powders

In this study, we have investigated the optical and photocatalytic properties of nanoparticulate (TiO₂)_x(ZnO)_1?x powders that were synthesised by mechanochemical processing. The objective was to establish the suitability of these powders for use as optically transparent ultraviolet light screening agents. It was found that the photocatalytic activity of single phase ZnO can be substantially reduced through the incorporation of TiO₂ at the cost of a comparatively minor decrease in optical transparency. The composition given by (TiO₂)_0.10(ZnO)_0.90 was characterised by a photocatalytic activity that was approximately 20% of that exhibited by the ZnO powder synthesised using similar processing conditions. These results demonstrate that (TiO₂)_x(ZnO)_1?x powders synthesised by mechanochemical processing are potentially useful as optically transparent ultraviolet light screening agents.     

Crystal structure and thermoelectric properties of Cu2Cd1−xZnxSnSe4 solid solutions

Cu₂Cd_1–xZn_xSnSe₄ solid solutions were synthesized, and their phase constitutions and thermoelectric properties were investigated. The solid solutions crystallized in the stannite-type structure for Zn contents x up to 0.65 and in the kesterite-type structure for 0.7 ≤ x ≤ 1.0. The lattice parameter a and cell volume V of the compounds decreased linearly with increasing x for both the stannite-type (0 ≤ x ≤ 0.65) and the kesterite-type (0.7 ≤ x ≤ 1) structures. The lattice parameter c decreased with increasing x for the compounds with the kesterite-type structure but increased for the compounds with the stannite-type structure. The c/a ratio increased with increasing Zn content, which indicated an weakening of the lattice distortion. The Seebeck coefficient tended to decrease with increasing Zn content, whereas the electrical conductivity and thermal conductivity increased. The figure of merit ZT increased with increasing x over the composition range of 0 ≤ x ≤ 0.60 and then fluctuated with a further increase in x. A maximum ZT of 0.23 was achieved for Cu₂Cd_0.4Zn_0.6SnSe₄ at 720 K.     

Tensile superplastic deformation of YBa2Cu3O7−x high-TC superconductors

The superplastic behavior of polycrystalline YBa₂Cu₃O_7−x was investigated. Tensile elongations above 85% were achieved for fine-grained (<1 μm) microstructures tested in the temperature range of 800–875°C and strain rates varying from 6×10⁻⁶ to 10⁻³/s. It is suggested that the dominant superplastic deformation mechanism is grain boundary sliding accommodated and controlled by interface reaction, characterized by a stress exponent of n=2, a grain size exponent of p=1.5, and an activation energy of Q_sp=515±104 kJ/mol. A Langdon–Mohamed deformation mechanism map was constructed. Overlaying the available experimental data onto the map, including the results from creep studies, gives an insight into the deformation mechanisms involved in high-temperature deformation of YBa₂Cu₃O_7−x.     

A Study of the Origin of Weak Ferromagnetism in Zn1−x Co x O

To study the origin of ferromagnetism in Zn_1?x Co _x O thin films, its thermal diffusivity, in addition to its magnetization measurements, were analyzed. Thin films of Zn_1?x Co _x O (x = 0.03) were deposited on Si (100) substrates through ultrasonic spray pyrolysis. Magnetization M(B) measurements at low temperature showed a hysteresis loop that indicated the existence of ferromagnetic ordering in Zn_0.97Co_0.03O. However, the magnetic moment per Co ion was much lower than expected. A comparison of M(T) measured at zero-field-cooled and field-cooled conditions showed a superparamagnetic-like behavior, with a blocking temperature of about 130 K. Temperature dependence on the thermal diffusivity of Zn_0.97Co_0.03O showed a pronounced lambda-shaped minimum at 130 K, which indicated the existence of a second-order phase transition at this temperature. The weak ferromagnetism in the Zn_0.97Co_0.03O with the Curie temperature of 130 K was ascribed to the uncompensated magnetic moment at the surface of CoO nanoclusters.