Substitution Of Ge For Si Research Articles

Phase structural characteristics and microwave dielectric properties of Ge-doped cordierite-based ceramics

The cordierite-based ceramics, Mg2Al4(Si1-xGex)5O18(MASG-x (x = 0, 0.1, 0.2, and 0.3) was successfully synthesized with Ge-substitution for Si, and subsequent analysis was conducted on their phase structural characteristics and microwave dielectric properties. Ge4+ substitution was discovered to be a key property-dependent factor. The analysis of phase fractions demonstrated the coexistence of orthorhombic and hexagonal phases in varying proportions across all compositions. Specifically, the hexagonal phase was identified as the predominant phase in Ge-substituted samples, reaching an optimal fraction of around 66.62% for MASG-0.2 and slightly decreasing to 63.45% for MASG-0.3. The correlation between the maximum quality factor (Qf)values and the hexagonal phase fraction exhibited strong consistency, thus playing a substantial role in explaining the origin of high Qf due to the related high symmetry structure of the hexagonal phase. An optimal Qf∼107,555 GHz and low dielectric constant (εr<5) was achieved by the MASG-0.2 sample sintered at 1380 °C.

Crystallization and Decomposition of Compounds with the Aurivillius Crystal Structure in the Bi2GeO5–Bi2SiO5 Pseudobinary Metastable System

The possibility of partial substitution of Si for Ge in the structure of Bi2GeO5 during synthesis from the melt and the effect of the substitution on the structure of the synthesized material have been studied. The microstructure of the synthesized compounds after their complete decomposition has been investigated. Using the phase powder X-ray diffraction- and optical microscopy methods, it has been found that metasta-ble phases of bismuth silicate and germanate with structures of the Aurivillius type form a continuous seriesof solid solutions. It is shown that a mixed structure composed of large Bi4Si(Ge)3O12 crystals and the Bi12Si(Ge)O20 + Bi4Si(Ge)3O12 point eutectic is obtained after the decomposition of compounds of the Bi2SiO5–Bi2GeO5 quasi-binary system, regardless of the percentage of substitution of Si for Ge. Upon slow heating up to annealing temperatures (at a rate of 13.5°C/min), a structure of decomposition that is more finely dispersed and uniform than the structure obtained upon rapid heating (when charg the material into an already preheated furnace), which is more coarsely grained and inhomogeneous. Moreover, regions with a large structure similar to a dendritic one can appear in the material when the contents of silicon and germa-nium oxides in the alloy are close to each other (20/30–30/20 mol %). Such regions differ slightly in chemical composition from the surrounding material and appear during both slow and rapid heating of the material to annealing temperatures.

Application of Ge/Si ratios to ultramafic alkaline rocks using a novel LA-ICP- MS/MS method

Germanium has, until recently, found limited interest in igneous and metamorphic rock studies due to analytical limitations, specifically low concentrations and many interferences. However, Ge and Ge/Si ratios have shown potential to distinguish between magma sources based on preferential substitution of Ge for Si in hydrous minerals such as amphibole, mica, and garnet. Here, we present a novel LA-ICP-MS/MS method that employs N2O as a reaction gas to analyse Ge as an oxide. We compare this method to previously used techniques (LA-ICP-MS and “H2” mode LA-ICP-MS), and find improvements in sensitivity and a reduction of interferences when measuring Ge as GeO. Application of this novel method to the Bilibin and Inagli alkaline intrusive complexes (Aldan Shield, Siberia) shows that Ge/Si ratios are lower in amphibole and mica, and higher in clinopyroxene in these alkaline rocks compared to similar minerals in basaltic and intermediate compositions. The differences are attributed to the mineral chemistry and further show the potential for the use of Ge/Si as a tracer.

Comparison of substitution of Si for Ge and Ga in Eu8Ga16Ge30: Magnetic measurement and fitting

Nominal Eu8Ga12Si4Ge30 and Eu8Ga16Ge26Si4 were synthesized by using ARC + MS method. XRD and EDS analysis confirmed that Si enters the lattice. Substitution of Si for Ga reduces TC from 35 K to 20 K. But the substitution of Si for Ge only has little effect on TC. It is about 30 K for Eu8Ga16Ge26Si4. The decrease of TC is beneficial to the increase of magnetic entropy change. So the maximum value of magnetic entropy change −ΔSMmax around TC under magnetic field change ΔH=3T increases to 7.6 and 6.1 J/kg﹒K for Eu8Ga12Si4Ge30 and Eu8Ga16Ge26Si4, respectively. They are both larger than the 6.0 J/kg﹒K of Eu8Ga16Ge30, especially Eu8Ga12Si4Ge30. So Ga is more important than Ge in terms of the physical properties of Eu8Ga16Ge30. The M − H data were fitted by Brillouin function. A series of parameters such as exchange parameter λ in Hexch = λM，the Lande factor g and total angular momentum quantum number J were obtained. Using these parameters, TC and −ΔSMmax were calculated and compared with the above values.

Electronic structure, mechanical and optical properties of ternary semiconductors Si1-xGexC (X = 0, 0.25, 0.50, 0.75, 1)

ABSTRACTThe electronic structure of silicon carbide with increasing germanium content have been examined using first principles calculations based on density functional theory. The structural stability is analysed between two different phases, namely, cubic zinc blende and hexagonal phases. The zinc blende structure is found to be the stable one for all the Si1-xGexC semiconducting carbides at normal pressure. Effect of substitution of Ge for Si in SiC on electronic and mechanical properties is studied. It is observed that cubic SiC is a semiconductor with the band gap value 1.243 eV. The band gap value of SiC is increased due to the substitution of Ge and the band gap values of Si 0.75 Ge 0.25 C, Si 0.50 Ge 0.50 C, Si 0.25 Ge 0.75 C and GeC are 1.322 eV, 1.413 eV, 1.574 eV and 1.657 eV respectively. As the pressure is increased, it is found that the energy gap gets decreased for Si1-x GexC (X = 0, 0.25, 0.50, 0.75, 1). The elastic constants satisfy the Born – Huang elastic stability criteria. The bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are also calculated and compared with the other available results.

The Si–Ge substitutional series in the chiral STW zeolite structure type

Ge substitution for Si in zeolites containing double-four-membered rings is far more complex than thought.

Post-Synthesis Stabilization of Germanosilicate Zeolites ITH, IWW, and UTL by Substitution of Ge for Al.

Germanosilicate zeolites often suffer from low hydrothermal stability due to the high content of Ge. Herein, we investigated the post-synthesis introduction of Al accompanied by stabilization of selected germanosilicates by degermanation/alumination treatments. The influence of chemical composition and topology of parent germanosilicate zeolites (ITH, IWW, and UTL) on the post-synthesis incorporation of Al was studied. Alumination of ITH (Si/Ge=2-13) and IWW (Si/Ge=3-7) zeolites resulted in the partial substitution of Ge for Al (up to 80 %), which was enhanced with a decrease of Ge content in the parent zeolite. In contrast, in extra-large pore zeolite UTL (Si/Ge=4-6) the hydrolysis of the interlayer Ge-O bonds dominated over substitution. The stabilization of zeolite UTL was achieved using a novel two-step degermanation/alumination procedure by the partial post-synthesis substitution of Ge for Si followed by alumination. This new method of stabilization and incorporation of strong acid sites may extend the utilization of germanosilicate zeolites, which has been until now been limited.

High thermal stability of red emission in Mn-doped benitoite-type strontium silicogermanate

We assessed the photoluminescence performance characteristics of Mn4+-doped tetragermanate and silicogermanate phases with a benitoite-type structure. We observed a visible red emission based on the 2E → 4A2 transition in the doped benitoite-type tetragermanate. The partial substitution of Si for Ge, resulting in SrGe3.495Mn0.005Si0.5O9, improved the internal quantum efficiency and thermal stability of the red emission. A possible explanation of the substitution effect was reasonably presented on the basis of the connectivity of luminescent polyhedral units and the decrease in the Franck–Condon off-set value in the benitoite structure.

Structural, electronic, and optical properties of ordered Si1−Ge C alloys: A first principles study

• Structural, electronic, and optical properties of ordered Si 1 − x Ge x C alloys by first principles calculations. • The lattice constants show a linear dependence on the composition x . • The bulk and shear moduli reduce linearly as the increase of composition x . • The indirect to direct band gap transition is result from the symmetry change. • It is proposed that the composition dependent refractive index follows a quadratic equation. The effect of germanium content on the structural, electronic, and optical properties of ordered Si 1 − x Ge x C alloys ( x = 0, 0.25, 0.5, 0.75, 1) has been systemically investigated in the present work by using first principles calculations based on the density functional theory. The calculated lattice parameters, bulk and shear moduli which exhibit linear dependences on the composition x follow the Vegard’s law and are fitted by linear interpolation. The electronic band structure calculations performed by the application of HSE03 functional reveal that Si 1 − x Ge x C alloys are all wide band gap semiconductors, among which Si 0.75 Ge 0.25 C and Si 0.25 Ge 0.75 C have direct band gaps. The substitution of Ge for Si changes the symmetry of zb-SiC unit cell, giving rise to the indirect to direct band gap transition. The composition dependent static optical functions, such as dielectric constants, refractive index and Plasmon energy are discussed.

Local lattice distortion induced by substitution of Si for Ge in Li2CaGe1−xSixO4 solid solutions

Possible reasons for essential differences in values of the total crystal field splitting and centroid shift of Ce3+ 5d configuration for isostructural Li2CaGeO4 and Li2CaSiO4 were analyzed by means of X-ray diffraction method and luminescent spectroscopy. It was found that the increase in Si concentration in Ce3+-doped Li2CaGe1−xSixO4 solid solutions leads to increasing of noncubic crystal field splitting parameter (∆) of the Ce3+ 5d configuration, indicating to an enhancement of distortion from the cubic symmetry of the calcium dodecahedral site upon going from Li2CaGeO4 to Li2CaSiO4. The results of X-ray diffraction analysis of Li2CaGe1−xSixO4 show that the linear decrease of the unit-cell parameters with increasing Si-content is followed by complex changes in the geometry of the Ca polyhedra. Changes in the electronic structure with the composition of the solid solutions are also discussed.

Evaluating Possibilities of Self-propagating High-temperature Synthesis (SHS) for Substitution of Ge for Si in MoSi2

Abstract Self-propagating high-temperature synthesis is used to study materials obtained from a Mo–Si–Ge system. Si1−xGex is known to be one of the most efficient thermoelectrics, but its use is limited by high price and scarcity of germanium, relatively low value of its ZT, and high working temperature. One way to increase its ZT consists of increasing the diffusion of the acoustic phonons by inserting silicide nanoinclusions of MoSi2 inside the Si1−xGex matrix. In this sense it is important to study the Mo(Si1−xGex)2 solid solutions.

Effect of Ge substitution for Si on the magnetic hyperfine field in LaMn2Si2 compound measured by perturbed angular correlation spectroscopy with 140Ce as probe nuclei

The effect of substitution of Ge for Si in LaMn2Si2 compound on the magnetic hyperfine field (Bhf) has been investigated by perturbed γ−γ angular correlation (PAC) spectroscopy using 140La(140Ce) as probe nuclei. This compound exhibits antiferromagnetism followed by a ferromagnetic ordering when temperature decreases. The behavior of the ferromagnetic transition when Ge gradually replaces Si, with concentrations of 20%, 40%, 80%, and 100% is discussed. PAC measurements were carried out in the temperature range from 15 K to 325 K. Results for LaMn2Si2 compound showed that the dependence of Bhf with temperature follows the expected behavior for the host magnetization and could be fitted by a Brillouin function for JMn = 5/2. However, the temperature dependence of Bhf for compounds when Si is gradually replaced by Ge showed a deviation from such a behavior, which gradually increases up to a strong deviation observed for LaMn2Ge2. This striking behavior was ascribed to the hybridization of d band of the host and f band of the Ce impurities, which is stronger when the unit cell volume increase as Si ions are substituted by Ge atoms.

Modulation of quartz-like GeO2structure by Si substitution: an X-ray diffraction study of Ge1−xSixO2(0 ≤x&lt; 0.2) flux-grown single crystals

The spontaneous nucleation by the high-temperature flux method of GeO2and SiO2-substituted GeO2(Ge1−xSixO2) compounds was improved to give single crystals free of hydroxy groups. The crystal structure and quality of these α-quartz-like piezoelectric materials were studied by single-crystal X-ray diffraction at room temperature. The refinements gave excellent final reliability factors, which are an indication of single crystals with a low level of defects. A good correlation was found between the silicon content in Ge1−xSixO2crystals determined through extrapolation from the inter-tetrahedral bridging angle and that found from energy-dispersive X-ray spectroscopy. The effect of germanium replacement by silicon on the distortion of the α-quartz-type GeO2structure was followed by the evolution of the intra-tetrahedral angle and other structural parameters. TheTO4(T= Si, Ge) distortion was found to be larger in α-GeO2than in α-SiO2and, as expected, the irregularity of theTO4tetrahedra decreased linearly as the substitution of Si for Ge increased.

Electrical Properties and Magnetic Response of Cobalt Germanosilicide Nanowires

The effects of partial substitution of Ge for Si in cobalt germanosilicide (CoSi(1-x)Ge(x) and Co(2)Si(1-x)Ge(x)) nanowires (NWs) on the electrical transport, magnetic properties, and magnetoresistance (MR) have been investigated. Cobalt germanosilicide NWs were synthesized by a spontaneous chemical vapor transport growth method. The Ge concentration can be selectively controlled from 0 to 15% and 0-50% for CoSi(1-x)Ge(x) and Co(2)Si(1-x)Ge(x) NWs, respectively, by varying the reaction temperature. Electrical measurements showed that the resistivities of CoSi(1-x)Ge(x) NWs are 90, 60, 30, and 23 μΩ-cm for x = 0, 0.01, 0.05, and 0.15, respectively. Therefore, the electrical resistivity of CoSi(1-x)Ge(x) NWs was found to decrease significantly with an increasing Ge concentration, which is believed to be a result of the band gap narrowing. On the other hand, the Co(2)Si(1-x)Ge(x) (x ≤ 0.5) NWs exhibited ferromagnetism at 300 K, which is attributed to the uncoordinated Co atoms on the NW surface and spin-glass behavior at low temperature. The highest MR response of Co(2)Si(1-x)Ge(x) NWs occurred at x = 0.5, where a MR ratio of 11.7% can be obtained at 10-25 K with a magnetic field of 8 T. The enhanced physical properties of cobalt germanosilicide NWs with Ge substitution shall lead to promising application in the fabrication of nanodevices, including spintronics and serving as the gate and interconnect material.

Influence of pressure on the magnetic behavior and the anomalous magnetoresistance inTb5Si3

The compound, Tb5Si3, crystallizing in Mn5Si3-type hexagonal structure, was recently reported by us to exhibit a sudden and huge enhancement in electrical resistivity (rho) at a critical magnetic field (H_cr) in the magnetically ordered state (<70 K) tracking isothermal magnetization (M) behavior. We have investigated the influence of external pressure (<15 kbar) and negative chemical pressure induced by Ge substitution for Si on M and rho as a function of temperature (5-300 K) and magnetic field (<120 kOe), with the primary aim of understanding the field-induced anomalies. Focussing on isothermal M and magnetoresistance (MR) at two temperatures, 5 and 20K, we find that this rho anomaly persists under external as well as negative chemical pressures, however with a large change in the H_cr. The pressure-derivative of H_cr is negative and this trend and the MR behavior at the H_cr are comparable to that observed in some Laves phase itinerant magnetic systems. On the basis of this observation, we speculate that the magnetic fluctuations induced at this critical field could be responsible for the MR anomal.ies

Crystal field interactions in DyFe 2Si 2 and DyFe 2Ge 2

Two sets of crystal field (CF) parameters have been proposed for DyFe 2Si 2, none of which could provide a simultaneous explanation of the available experimental data, particularly at low temperatures (below 100 K). The set derived from magnetic studies could not even explain the thermal variation of the magnetic specific heat reported in the same work. Although the set of CF parameters, obtained from a fit to the Mossbauer spectra, could provide a fairly good explanation of the thermal variation of the magnetic susceptibilities along the c-axis, it could not explain the observed thermal variation of other reported experimental findings. In the present work, an appraisal of the CF parameters proposed earlier has been done and a set of CF parameters has been derived, which provide a simultaneous explanation of all the available experimental data. The effect of substitution of Ge for Si on the magnetic properties and the magnetic specific heat of DyFe 2Si 2 has been studied in the framework of one electron crystal field model. The inelastic neutron scattering studies and EPR measurements are required to check the predicted Stark energies and the paramagnetic resonance g-values.

Magnetic, magnetothermal, and magnetotransport properties in SmMn2Si2−xGex compounds

The effect of Ge substitution for Si in SmMn2Si2−xGex compounds has been studied. The Sm ordering temperature is found to be much larger in the compound with x=2, as compared to the compounds with x=0 and 1. The increase in the intralayer Mn–Mn distance is attributed to this variation. Among these three compounds, SmMn2Ge2 is found to show reentrant ferromagnetism at low temperatures. The magnetic contribution to the heat capacity has been calculated in all the three compounds. The splitting of the ground state multiplet has been estimated by fitting the magnetic part of the heat capacity data, using the Schottky formula. The isothermal magnetic entropy change is found to remain the same for x=0 and 1 but decreases in the compound with x=2, though the nature of magnetic transition changes from second order to first order, as x is increased from 0 to 2. The electrical resistivity increases with Ge concentration. The excess resistivity in the antiferromagnetic region has been calculated.

Crystal chemistry of layered carbide, Ti 3(Si 0.43Ge 0.57)C 2

The crystal structure of a layered ternary carbide, Ti 3(Si 0.43Ge 0.57)C 2, was studied with single-crystal X-ray diffraction. The compound has a hexagonal symmetry with space group P6 3/mmc and unit-cell parameters a=3.0823(1) Å, c=17.7702(6) Å, and V=146.21(1) Å 3. The Si and Ge atoms in the structure occupy the same crystallographic site surrounded by six Ti atoms at an average distance of 2.7219 Å, and the C atoms are octahedrally coordinated by two types of symmetrically distinct Ti atoms, with an average C–Ti distance of 2.1429 Å. The atomic displacement parameters for C and Ti are relatively isotropic, whereas those for A (=0.43Si+0.57Ge) are appreciably anisotropic, with U 11 (= U 22) being about three times greater than U 33. Compared to Ti 3SiC 2, the substitution of Ge for Si results in an increase in both A–Ti and C–Ti bond distances. An electron density analysis based on the refined structure shows that each A atom is bonded to 6Ti atoms as well as to its 6 nearest neighbor A site atoms, whether the site is occupied by Si or Ge, suggesting that these bond paths may be significantly involved with electron transport properties.

Substitutional effect on the transport properties of MnSi

We report the transport properties, including electrical resistivity ( ρ) and Seebeck coefficient ( S) of Ge-substituted MnSi 1− x Ge x (with x=0, 0.02, 0.05, and 0.10) alloys as a function of temperature between 10 and 300 K. It was found that the partial substitution of Ge at Si site has a surprisingly weak effect on the ferromagnetic transition temperature T C in MnSi, indicating that the negative chemical pressure produced by the substitution of larger ion Ge in place of Si is unable to significantly influence the magnetic ordering. In addition, the temperature-dependent Seebeck coefficient shows similar behaviour for theses alloys, which suggests that the electronic density of states (DOS) of MnSi near the Fermi level is essentially unaffected by Ge substitution for Si.

Superconducting phases and quantum criticality in CeCu2Si2

For the prototypical heavy-fermion (HF) metal CeCu2Si2 superconductivity extends to surprisingly high pressures (PO10 GPa), quite different from other Ce-based HF superconductors, like CePd2Si2, where superconductivity is confined to a narrow P-range centered around an antiferromagnetic quantum critical point (QCP). By deliberately reducing the HF mean free path, i.e. by moderate Ge-substitution for Si, superconductivity could be weakened and two distinct superconducting regimes could be established at low and high P, respectively. The low-P regime is centered at a magnetic QCP. The nature of the magnetic phase could recently be unraveled with the aid of neutron diffractometry and appears to be an incommensurate low-moment spin-density-wave phase. q 2005 Published by Elsevier Ltd.