Effect Of Ge Substitution Research Articles

The effect of Ge substitution on phase transformation and magnetic properties of MnBi alloys

The Mn55Bi45-xGex intermetallic compound with x ≤ 4 was prepared and compared by annealed ribbons and powder metallurgy. Substituting Ge in the MnBi alloy significantly alters the phase transformation temperatures, enhances the coercivity (Hc), and improves the squareness. As the Ge concentration increased from 0 at.% to 4 at.%, both the crystalline size of low-temperature phase MnBi in annealed ribbons and ball-milled powders demonstrated a gradual decrease, while lattice strain exhibited an upward trend. The Hc of Mn55Bi41Ge4 powder reaches 14.1 kOe, which is 33 % higher than that of pure MnBi powder, making MnBi-Ge an ideal candidate magnet for the next generation of rare-earth-free magnets.

Effect of Ge substitution on the magnetocaloric effect and exchange bias in Mn–Ni–Sn-Ge alloys: The role of Mn–Mn distance

Abstract The effect of Ge substitution on the phase transitions, magnetocaloric effect, and exchange bias is studied in Mn50Ni40Sn10-xGex alloys by structural and magnetic analysis. Due to the lattice contraction induced by Ge substitution, the martensitic transformation temperature increases gradually, and the reentrant spin glass ground state is suppressed at x = 5 where zero-field-cooled exchange bias (ZEB) emerges. The maximum values of magnetic entropy change and ZEB are 19.2 J/kg·K for the field change of 5 T and 1.49 kOe at 10 K, which are achieved in Mn50Ni40Sn8Ge2 and Mn50Ni40Sn4Ge6, respectively. Importantly, the second-nearest Mn–Mn distance is found to be a key parameter affecting the magnetization change across the martensitic transformation and the ground state of these alloys. This work sheds new light on understanding the magnetism in Ni–Mn-based ferromagnetic shape memory alloys.

Synthesis and processing effects on magnetic properties in the Fe5SiB2 system

The effects of Ge substitution and synthesis via rapid solidification on the structure and magnetic character of the intermetallic Fe5SiB2 (5-1-2) system were determined, with the objective to investigate the potential of Fe5(Si0.75Ge0.25)B2 as a new permanent magnet material. Samples were made by arc-melting/annealing as well as by melt-spinning/annealing and were evaluated by probing the structure, composition, and magnetic response. Results indicate that the tetragonal Cr5B3 crystal structure, large saturation magnetization (Ms = 153.8 emu/g) and Curie temperature (Tc = 784 K) of the parent Fe5SiB2 phase may be preserved by substituting up to 25 at % of Si in the lattice with Ge. The room-temperature magnetocrystalline anisotropy constant of a Ge-substituted alloy of nominal composition Fe5(Si0.75Ge0.25)B2 was evaluated as K1 = 5 × 106 ergs/cc using the law of approach to saturation and is the largest reported to date within the 5-1-2 materials system. As a result of compositional modification, the spin reorientation observed in Fe5SiB2 is greatly suppressed from 172 K to 60 K. A comparison of the 5-1-2 phase evolution when synthesized by standard casting and by rapid solidification indicates that melt spinning is a simpler and more expeditious synthesis method relative to previously reported solid-state reaction methods.

Effects of Ge substitution on morphology and electrical properties of Cu2Sn(S,Se)3 bulk at a fixed Se/[Se+S] composition

Ge-substituted Cu2Sn(S,Se)3 bulks with Cu2(Sn1-xGex)(S,Se)3 formula at x = 0, 0.25, 0.50, 0.75, and 1.0 were synthesized by reactive liquid phase sintering, where the heating process was held at 200°C for 20min before reaching the sintering temperature of 600°C for 30min. In the presence of volatile Sb2S3 sintering aid, the effects on densification, grain boundary, crystalline size, and electrical properties of Ge-substitution were investigated. Cu2(Sn1-xGex)(S,Se)3 showed p-type behavior for all x values. It was found that the mobility was increased sharply and carrier concentration was decreased rapidly as the x-value was increased. The electrical conductivities were found to be 14.0, 22.7, 36.8, 126, and 153S/cm at x = 0, 0.25, 0.50, 0.75, and 1.0, respectively. X-ray diffraction (XRD) peaks were shifted to the higher angle and band gaps increased upon successive increasing of the Ge/[Ge+Sn] fraction being 1.19, 1.21, 1.22, 1.24, and 1.26eV at x = 0, 0.25, 0.50, 0.75, and 1.0, respectively. The studies of Ge-x-CTSSe bulks were based on GeSn defects and supported by the data of morphological, structural, electrical, and optical properties.

Effects of Ge substitution on thermoelectric properties of CrSi2

Polycrystalline Cr(Si1−xGex)2 samples were prepared using arc melting and spark plasma sintering methods. Single-phase Cr(Si1−xGex)2 samples were obtained for the compositional range of 0 ≤ x ≤ 0.015 and the lattice parameters monotonically increased with x. In the range of single phases, the electrical conductivity and Seebeck coefficient increased and decreased with increasing x, respectively. The partial substitution of Ge effectively reduced the thermal conductivity to ∼80%, which resulted in the increase in the ZT of Cr(Si1−xGex)2 samples from 0.16 (x = 0) to 0.25 (x = 0.015) at 600 K. From the results of first-principles calculation for transport properties, it can be concluded that the origin of the increase in electrical conductivity and the decrease in Seebeck coefficient of Ge-substituted samples is the decrease in carrier effective mass.

Effects of Ge substitution in GeTe by Ag or Sb on the Seebeck coefficient and carrier concentration derived fromTe125NMR

GeTe, a self-doping $p$-type semiconductor where the high free hole concentration is determined by Ge vacancies is a well-known base for high-efficiency $\mathrm{A}{\mathrm{g}}_{x}\mathrm{S}{\mathrm{b}}_{x}\mathrm{G}{\mathrm{e}}_{50\ensuremath{-}2x}\mathrm{T}{\mathrm{e}}_{50}$ (a tellurium-antimony-germanium-silver series) thermoelectric materials. Here it is shown that the replacement of Ge by Ag in GeTe (a $\mathrm{A}{\mathrm{g}}_{x}\mathrm{G}{\mathrm{e}}_{50\ensuremath{-}x}\mathrm{T}{\mathrm{e}}_{50}$ system) significantly decreases the Seebeck coefficient, whereas the replacement by Sb $(\mathrm{S}{\mathrm{b}}_{x}\mathrm{G}{\mathrm{e}}_{50\ensuremath{-}x}\mathrm{T}{\mathrm{e}}_{50})$ increases it. These effects can be attributed to a change in carrier concentration and consistent with $^{125}\mathrm{Te}$ NMR spin-lattice relaxation measurements and NMR signal position, which is mostly dependent on the Knight shift. Opposite changes in carrier concentration in $\mathrm{A}{\mathrm{g}}_{x}\mathrm{G}{\mathrm{e}}_{50\ensuremath{-}x}\mathrm{T}{\mathrm{e}}_{50}$ and $\mathrm{S}{\mathrm{b}}_{x}\mathrm{G}{\mathrm{e}}_{50\ensuremath{-}x}\mathrm{T}{\mathrm{e}}_{50}$ can be explained by different valence electron configurations of Ag and Sb compared to that of Ge, which results in a different local electron imbalance and/or in a change in Ge vacancy formation energy and affects the total carrier concentration. Comparison of our data for GeTe, $\mathrm{A}{\mathrm{g}}_{2}\mathrm{G}{\mathrm{e}}_{48}\mathrm{T}{\mathrm{e}}_{50}$, and $\mathrm{S}{\mathrm{b}}_{2}\mathrm{G}{\mathrm{e}}_{48}\mathrm{T}{\mathrm{e}}_{50}$ with those for $\mathrm{A}{\mathrm{g}}_{2}\mathrm{S}{\mathrm{b}}_{2}\mathrm{G}{\mathrm{e}}_{46}\mathrm{T}{\mathrm{e}}_{50}$ shows that the effects from Ag and Sb compensate for each other and supports the formation of $[\mathrm{Ag}+\mathrm{Sb}]$ atomic pairs suggested earlier based on theoretical calculations.

Magnetocaloric properties, exchange bias, and critical behavior of Ge substituted Ni50Mn36Sn14 Heusler alloys

The effect of Ge substitution on the magnetic, magnetocaloric, and exchange bias properties of Heusler alloy system Ni50Mn36Sn14-xGex (x = 1, 2) has been investigated. With the increase of Ge content, the cell volume decreases due to the smaller Ge radius and the martensitic transition temperature increases, while the Curie temperature of the austenite phase shows a small decrease. Metamagnetic behavior is observed in the low temperature magnetization isotherms for x = 1, whereas it is less pronounced in x = 2. The maximum magnetic entropy changes associated with the martensitic transition are 7.8 J/kg K and 2.3 J/kg K for x = 1 and 2, respectively, for a field change of 5 T. Relative cooling power is found to be more in the vicinity of the Curie temperature of the austenite phase, compared to that at the martensitic transition temperature in both x = 1 and 2. At low temperatures, both the samples exhibit exchange bias effect, with x = 2 showing higher value of exchange bias field. This is ascribed to the coexistence of ferromagnetic and antiferromagnetic interactions in these alloys. Further, the critical behavior of the austenite phase of both the alloys is studied and the values of the critical exponents are found to be different from the mean field values, which is attributed to the magnetic inhomogeneity originated due to Ge substitution.

Effects of Ge substitution on the structural and physical properties of CuFeO2 delafossite oxide

Delafossite CuFe1−xGexO2 (0.0 ≤ x ≤ 0.1) semiconductors were synthesized by solid-state reaction. The effects of Ge concentration on microstructural, optical, magnetic and electrical properties were investigated. X-ray diffraction (XRD) analysis results reveal the delafossite structure of all the samples. The lattice spacing of CuFe1−xGexO2 decreased with increasing substitution of Ge at the Fe site. The optical properties measured at room temperature by UV–visible spectroscopy showed an absorption peak at 283 nm (4.38 eV). The corresponding direct optical band gap was found to decrease with increasing Ge content (from 3.69 eV for x = 0 to 3.61 eV for x = 0.10), exhibiting transparency in the visible region. The magnetic hysteresis loops measured at room temperature showed that the Ge-doped CuFeO2 samples exhibit ferromagnetic behavior. The Curie temperature suggests that ferromagnetism originates from CuFe1−xGexO2 matrices. The substitution of Fe3+ by Ge4+ produces a mixed effect on the magnetic properties of CuFeO2 delafossite oxide. The resistivity of CuFe0.99Ge0.01O2 was observed to be ∼0.1 Ω·cm at room temperature.

Effect of Ge substitution on carrier mobilities and thermoelectric properties of sintered p-type Ba8Ga16+xSn30−x−yGey with the type-VIII clathrate structure

Ge substitution for Sn in Ba8Ga16Sn30 was attempted in order to improve its thermoelectric properties. Since the melting point was raised by the substitution, the sintering temperature could be increased. The resultant sintered samples exhibited higher thermal stabilities and fewer trapping state densities at grain boundaries, which weakened grain boundary scattering for carriers. For example, the Ba8Ga16.4Sn25.0Ge4.6 and Ba8Ga16.9Sn19.8Ge9.3 samples had larger room temperature mobilities of 6.7 cm2 V−1 s−1 and 13.3 cm2 V−1 s−1, respectively, than that of 2.3 cm2 V−1 s−1 of the Ba8Ga16.6Sn29.4 sample. Consequently, these Ge-substituted samples had higher figures-of-merit maxima of 0.62 at 550 K and 0.63 at 600 K, respectively, than that of 0.36 at 500 K for the Ba8Ga16.6Sn29.4 sample.

Effect of Ge substitution on excess conductivity and infrared absorption of Tl0·85Cr0·15Sr1−xGexCaCu2O7 superconducting ceramics

Samples of Tl0·85Cr0·15Sr2−xGexCaCu2O7−δ (x = 0–0·3) were successfully synthesised using the solid state synthesis method. Electrical resistance measurements showed that the zero critical temperature value Tc zero was in the range of 90–98 K for x = 0–0·15 and in the range of 60–78 K for x = 0·2–0·3. Analysis of excess conductivity behaviour based on the Aslamazov–Larkin model for the unsubstituted x = 0 compound revealed a two-dimensional fluctuation behaviour. Substitution of Ge in Tl0·85Cr0·15(Sr2−xGex)CaCu2O7−δ induced two- to three-dimensional transition with the highest transition temperature T2D–3D observed at x = 0·10. In this study, the calculation using the Lawrence–Doniach model showed that the sample with the lowest anisotropy was x = 0·08. Fourier transform infrared absorption together with X-ray diffraction data analyses indicate increasing CuO interplane coupling with Ge substitution, which is suggested to cause sustenance of the high Tc zero and metallic normal state behaviour for x = 0–0·15.

Improved Dielectric Properties of Low-Temperature-Sintered (Ba,Sr)TiO3-Based Ceramics by Ge Substitution

Multilayer microwave dielectric materials with low sintering temperature are required for microwave phase shifters, filters, and true-time delay devices. We investigated the sintering and dielectric properties of (Ba0.6Sr0.4)(Ti1-xGex)O3 (BSTG; 0.05≤x≤0.3) ceramics. As the Ge concentration was increased, the lattice constant of BSTG ceramics decreased, and Ba2Ge2TiO8, which is the liquid phase at low temperature, was formed. Ba2Ge2TiO8 liquid phase may increase the sintering density. The effect of Ge substitution is the decrease in the sintering temperature from over 1400 to 1150 °C in BST system ferroelectric ceramics. With increasing Ge concentration, the dielectric constant decreased from 2190 to 530, and the dielectric loss decreased up to 0.001 (at 1 MHz) with sintering at 1150 °C for 2 h. When Ge was substituted at 0.05 and 0.1 mol of Ti in the BST at 1150 °C, the dielectric constant, dielectric loss, tunability, Curie temperature, and figure of merit were 2184 and 1529, 0.002 and 0.001, 27 and 23%, -11 and -18 °C, and 135 and 230, respectively. These compositions show microwave dielectric properties comparable to those of (Ba0.5Sr0.5)TiO3 ferroelectrics, which are the important materials for tunable devices such as varactors, phase shifters, and frequency agile filters.

Effects of Ge substitution on the thermoelectric properties and pseudogap characteristics ofFe2VGa

We report the effects of partial substitution of Ge onto the Ga sites ofFe2VGa by measuring electrical resistivity, Seebeck coefficient and thermal conductivity as afunction of temperature. It is found that Ge substitution effectively dopes electrons to thesystem and thus causes a dramatic decrease in the electrical resistivity. The Seebeckcoefficient changes sign from positive to negative upon replacing Ga by Ge, which is ingood agreement with a simple band filling picture. In addition, the magnitudeof the Seebeck coefficient gradually increases and attains a maximum value of85 µV K−1 at around120 K for Fe2VGa0.9Ge0.1. Such a variation of Seebeck coefficient can be understood by means of rigidband-like shifting of the Fermi level across the pseudogap. The thermalconductivity is also reduced and a detailed analysis based on the Debyeapproximation indicates that the extrinsic disorder introduced by Ge substitution inFe2VGa has a minor contribution to the point defect scattering. Other lattice imperfections, such asantisite disorder, may be the main source for the point defect scattering whichshows no systematic variation with Ge concentration. While the thermoelectricperformance improves with the partial substitution of Ge, the largest figure-of-merit(ZT) value among these presently investigated alloys is still an order of magnitude lower thanthe conventional thermoelectric materials.

Effect of Ge substitution for Si on the anomalous magnetocaloric and magnetoresistance properties of GdMn2Si2 compounds

The effect of Ge substitution on the magnetization, heat capacity, magnetocaloric effect, and magnetoresistance of GdMn2Si2−xGex (x=0, 1, and 2) compounds has been studied. The magnetic transition associated with the Gd ordering is found to change from second order to first order on Ge substitution. Magnetic contributions to the total heat capacity and the entropy have been estimated. Magnetocaloric effect has been calculated in terms of adiabatic temperature change (ΔTad) as well as isothermal magnetic entropy change (ΔSM) using the heat capacity data. The temperature dependence of the magnetocaloric effect in all the three compounds have shown broad peaks. The maximum values of ΔSM and ΔTad for GdMn2Ge2 are found to be 5.9J∕kgK and 1.2K, respectively. The magnetoresistance is found to be very large and positive with a maximum value of about 22% in the case of GdMn2Ge2. In the other two compounds also, the magnetoresistance is predominantly positive, except in the vicinity of the Gd ordering temperature. The anomalous nature of the magnetocaloric effect and the magnetoresistance has been attributed to the canted magnetic structure of these compounds.

Triplet states at an O vacancy in α-quartz

The energy landscape of an \ensuremath{\alpha}-quartz O vacancy in the lowest triplet state is investigated. Four local minima are identified and geometries, total energies, and electron paramagnetic resonance (EPR) parameters are obtained. On the basis of calculated values for the magnetic dipole interaction between the electrons two of the structures are identified with known triplet centers detected by EPR. The effect of Ge substitution is studied, and it is concluded that Ge impurities in silica act as traps for dangling bonds with a trapping energy of $\ensuremath{\sim}1.5 \mathrm{eV}$ relative to Si ions.

A neutron diffraction study of HfFe 6Ge 6-type LuMn 6Ge 6− xGa x compounds ( x=0.4, 0.7 and 1.0)

The LuMn 6Ge 6− x Ga x compounds ( x=0.4, 0.7, 1.0) were studied by magnetization measurements and neutron diffraction. The LuMn 6Ge 5Ga compound is ferromagnetic in its whole ordered range ( T c=352 K). The Mn moments (2.02(8) μ B at 2 K) are close to the (001) plane. The LuMn 6Ge 5.3Ga 0.7 compound displays a Néel point at 372 K and is helimagnetic in the whole temperature range investigated by neutron diffraction (2–300 K). At 2 K, the normal to the helical plane makes an angle of 45(1)° with the c-axis, and the moment is refined to μ Mn=2.36(5) μ B. The LuMn 6Ge 5.6Ga 0.4 compound displays a Néel point at 451 K. Neutron diffraction indicates that, above T t∼290 K, the compound is colinear antiferromagnetic, as characterized by a doubling of the c-axis and with a moment direction parallel to the c-axis. Below T t′∼230 K, the compound becomes helimagnetic. At 2 K, the normal to the helical plane makes an angle of 42(1)° with the c-axis, and the moment is refined to μ Mn=2.24(4) μ B. The corresponding q z component of the propagating vector [0.2082(4)] at 2 K is significantly different from that measured in the LuMn 6Ge 5.6Ga 0.4 compound [0.1067(6)]. The effects of Ge substitution on the magnetic properties are discussed.

Phase analysis in the Ni–Ge–P system by electron diffraction

Abstract The structural analysis by convergent-beam electron diffraction (CBED) of two new ternary phases Ni(P,Ge)x where x ≈ 1 and 2 is described. One phase, with approximate composition NiP0·6Ge0·2 and initially identified within metal contacts to InP millimetre-wave devices, contained an incommensurate displacive modulation of a NiAs-type subcell (a = 3·42 Å c=4·89 Å). Two related parallel wave-vectors q1 = (1/3 + δ)g and q 2 = (1/3 - 2δ)g were observed, where g = a∗ + b∗ and δ varied between 0·012 and 0·019 in adjacent domains defined by the three possible 〈 1120〉 directions for q. The domains were comparatively large (0·5–5·0 μm) and were separated by polygonal boundaries parallel to the {1120) and {1100} planes. Large-angle dark-field CBED patterns taken around clusters of incommensurate reflections were used to recognize dynamical one- and two-dimensional diffraction routes contributing to the intensities of q1 and q2 and to assign primarily transverse and longitudinal characters to the wave-vectors, respectively. The second phase, with approximate composition NiP1·8Ge0·2 was a marcasite, whereas binary NiP2 crystallizes in either pyrite or monoclinic forms. The lattice parameters (a=4·46 Å b=5·54 Å c=3·41 Å, space-group Pnnm) and the anion 4(g) parameters (x=0·197, y=0·379) were measured on the [111] zone axis from the geometry and intensities of first-order Laue zone reflections. Bond lengths are compared with the almost isoelectronic FeS2 compounds, and the effect of Ge substitution in Ni–P binary compounds is discussed.