Effects Of Ge Doping Research Articles

Physical mechanism of Ge doping enhanced Ruddlesden-Popper structure quasi-2D Sr<sub>3</sub>Sn<sub>2</sub>O<sub>7</sub> ceramic hybrid improper ferroelectricity

Hybrid improper ferroelectricity with quasi-two-dimensional (quasi-2D) structure has attracted much attention recently due to its great potential in realizing strong magnetoelectric coupling and room-temperature multiferroicity in a single phase. However, recent studies show that there appears high coercive field and low remnant polarization in ceramics, which severely hinders the applications of this material. In this work, high-quality Sr<sub>3</sub>Sn<sub>2</sub>O<sub>7</sub> and Sr<sub>3</sub>Sn<sub>1.99</sub>Ge<sub>0.01</sub>O<sub>7</sub> ceramics with a Ruddlesden-Popper (R-P) structure are successfully prepared, and their crystal structures and electrical properties are investigated in detail. It is found that the Sr<sub>3</sub>Sn<sub>2</sub>O<sub>7</sub> ceramic exhibits a lower coercive field that is close to that of Sr<sub>3</sub>Sn<sub>2</sub>O<sub>7</sub> single crystal. Moreover, via a small amount of Ge doping, the polarization reaches 0.34 μC/cm<sup>2</sup> for Sr<sub>3</sub>Sn<sub>2</sub>O<sub>7</sub> and 0.61 μC/cm<sup>2</sup> for Sr<sub>3</sub>Sn<sub>1.99</sub>Ge<sub>0.01</sub>O<sub>7</sub>. Combining crystal lattice dynamic studies, we analyze the Raman and infrared responses of the samples, showing the information about the tilting and rotation of the oxygen octahedra in the samples. The improved ferroelectricity after doping may be attributed to the increased amplitude of the tilt mode and the reduced amplitude of rotation mode. Besides, the enhanced ferroelectric properties through Ge doping and its mechanism are further investigated by the Berry phase approach and the Born effective charge method. Furthermore, via the UV-visible spectra, the optical bandgap is determined to be 3.91 eV for Sr<sub>3</sub>Sn<sub>2</sub>O<sub>7</sub> ceramic and 3.95 eV for Sr<sub>3</sub>Sn<sub>1.99</sub>Ge<sub>0.01</sub>O<sub>7</sub> ceramic. Using the Becke-Johnson potential combined with the local density approximation correlation, the bandgap is calculated and is found to be in close agreement with the experimental result. And the electronic excitations can be assigned to the charge transfer excitation from O 2p to Sn 5s (Ge 4s). The effects of Ge doping on the ability of Sr<sub>3</sub>Sn<sub>2</sub>O<sub>7</sub> to gain and lose electrons and the bonding strength of Sn-O bond are analyzed via two-dimensional charge density difference. In conclusion, this study provides insights into the synthesis method and modulation of ferroelectric properties of hybrid improper ferroelectrics Sr<sub>3</sub>Sn<sub>2</sub>O<sub>7</sub>, potentially facilitating their widespread applications in various capacitors and non-volatile memory devices.

Tunable electronic and optical properties of two-dimensional ZnSe/AlAs van der Waals heterostructure

Heterostructure formed by combining a single material has outstanding electronic and optical properties, and therefore it has received great attention. In this work, we constructed a ZnSe/AlAs heterostructure. Moreover, based on first-principles calculations of density functional theory (DFT), its stacking orders, electronics, optical properties and the effects of Ge doping on the heterostructure were studied. The results show that the ABI (the Zn atoms of the ZnSe layer are above the As atoms of the AlAs layer) stacking with an interlayer spacing of 2.75 A is thermodynamically stable. Additionally, it has a direct bandgap of 0.986 eV which is less than the bandgap of the ZnSe and AlAs monolayers. By changing the interlayer distance, the external electric field and the plane strain, the bandgap of the ZnSe/AlAs heterostructure exhibits tunability and is accompanied by a semiconductor–metal transition. Importantly, compared with the single layer, the light absorption capacity of the ZnSe/AlAs heterostructure is significantly enhanced, especially in the ultraviolet region. The addition of Ge will shrinks the bandgap of the ZnSe/AlAs heterostructure and caused a direct–indirect transition. The light absorption peak of the heterostructure was slightly red-shifted, which was helpful to improve its absorption in the visible light region. The above results indicate that the ZnSe/AlAs heterostructure is expected to be a good candidate for optoelectronic devices and nanoelectronics.

The effects of Ge doping on the thermoelectric performance of p-type polycrystalline SnSe

Ge doping enables to enhance the thermoelectric figure of merit of SnSe..

Nanomagnetism in Ge-Doped Narrow CNTs

By carrying out density functional theory (DFT) calculations, we studied the effects of Gedoping on the geometrical, electronic, and magnetic properties of carbon nanotubes (CNTs). Three different doping configurations were considered. All of these configurations were stable upon relaxation. It was found that the formation energies of Ge-doped zigzag nanotubes increased with increasing tube diameters, indicating that the doping of Ge into narrower CNTs was more energetically favorable. In the presence of impurity, the electronic properties of small gap semiconducting nanotubes could be changed and the band gap be removed, but the metallic (5, 5) nanotube remained metallic after doping. Spontaneous magnetization was found to be induced in doping Ge nanotubes. The occurrence of ferromagnetism in the absence of transition-metal atoms arose mainly from the Ge-p states and was partially due to C p-orbitals. The magnetic moments of Ge atoms vary with the radius and chirality of nanotubes and their adsorbing sites.

Effects of Ge Doping on Electrochemical Migration, Corrosion Behavior and Oxidation Characteristics of Lead-Free Sn-3.0Ag-0.5Cu Solder for Electronic Packaging

Due to lead-free pressure, Sn-Ag-Cu solder is regarded as the potential candidate. However, higher melting point and faintish soldering restrict its wide application. Metal or rare earth metal doping can improve its soldering. In this thesis, Ge doping in Sn-3.0Ag-0.5Cu (SAC) solder were discussed. Effect of metal Ge doping on electrochemical corrosion behavior of lead-free SAC solder in 3wt.% NaCl solution were investigated by potentiodynamic polarization measurement. The electrochemical migration（ECM）attributed to dendrites growth were employed by the salt immersion experiment, and the oxidation characteristic was researched by thermo gravimetric analysis(TGA). The surface morphology and elemental composition of various elements in the doped solder were determined by analyzing the corrosion product or dendrites formed on the specimen by SEM, EDAX techniques. The results showed that the dendrite growth can be accelerated after Ge doping comparing to Sn-3.0Ag-0.5Cu solder. The shapes of dendrites were completely different before and after Ge doping, the fore looked like as tree leaves, the latter looked like little stem, all dendrites grown from different kind of material can be well differentiated by the help of their fractal dimension. EDAX result showed that the content on dendrites of Sn-3.0Ag-0.5Cu solder doping with Ge were mainly Sn, only little Cl- and Na+. Corrosive experiment showed that the corrosive current density (Icorr) increased with Ge content increasing when the percent content of Ge was less than or equal to 1%, the contrary effect suitable to that Ge doping larger than 1%. TGA result showed that Ge doping could improve the anti-oxidation capacity of SAC solder comparing to no doped solder. It provided a good technical support to develop a new lead-free solder substituting for Sn-37Pb.

Effects of Ge doping on the thermoelectric properties of TiCoSb-based p-type half-Heusler compounds

Ge-doped TiCoSb-based half-Heusler compounds, TiCoGexSb1−x (x = 0–0.2), were prepared by arc melting and spark plasma sintering (SPS). The electrical conductivity, Seebeck coefficient and thermal conductivity were measured from room temperature to 850 K. The Seebeck coefficient changed from negative to positive by Ge doping, and the electrical conductivity increased with increasing Ge content. The lattice thermal conductivity for TiCoGexSb1−x is considerably reduced, because the point defects induced by Ge substitution for Sb intensively scatter the thermal phonons. The mass fluctuation part Γmass and strain field fluctuation part Γstra were estimated, and it was found that the reduction of lattice thermal conductivity is mainly attributed to the strain field fluctuation. Ge doping improved the thermoelectric figure of merit ZT of TiCoSb and the maximum ZT value of 0.16 was obtained for TiCoGe0.15Sb0.85 sample at 850 K.

Effects of Ge Doping on Micromorphology of MnSi in MnSi∼1.7 and on Their Thermoelectric Transport Properties

MnSi layers in Ge-doped MnSi∼1.7 increased with increasing Ge content up to x=0.00133, began to break at x=0.00265 and finally disappeared at x=0.00530. An experimental equation for the growth of MnSi was proposed for the interval between the MnSi layers and amount of doped Ge content. The crystallinity of Ge-doped MnSi∼1.7 increased initially with increasing doped Ge content and saturated at high Ge content. Thermoelectric transport properties along the c-axis of Ge-doped MnSi∼1.7 were measured as a function of Ge content at room temperature. Electrical conductivity and thermoelectric power of Ge-doped MnSi∼1.7 were compared to those of Al-doped MnSi∼1.7 in our previous work. A maximum in the electrical conductivity and a minimum in the thermoelectric power of Ge-doped MnSi∼1.7 were observed at x=0.00133, reflecting a change in hole density which was influenced by the volume ratio of MnSi. Hole mobility depended on the existence of MnSi layers and/or of interfaces between MnSi∼1.7 and MnSi and on the crystallinity of MnSi∼1.7. The thermal conductivity of Ge-doped MnSi∼1.7 had a maximum at x=0.00053. The increase in thermal conductivity at low Ge doping can be explained by the increase in the amount of MnSi segregated in doped MnSi∼1.7, while the decrease at high Ge content was caused by the increase in phonon scattering of Ge. A maximum figure of merit of Ge-doped MnSi∼1.7 was obtained at x=0.00974, reflecting a maximum power factor.

The effect of thermal treatment on the magnetic properties of Ge-doped FeNbB alloys

The effects of Ge doping on the magnetic properties of nanocrystalline FeNbB ribbons are investigated. For amorphous Fe80Nb10Ge3B7 alloy, three crystallization processes are observed when heated from room temperature to 1173 K. At 973 K, a harder magnetic phase is formed, which brings about a constricted hysteresis loop. A large increase of relaxation frequency and a dramatic drop of permeability of 973 K-annealed Fe80Nb10Ge3B7 alloy are observed. The presence of Nb is essential for the nanocrystallization of α-Fe grains. If Nb is replaced by Ge completely, the thermal treatment will lead to the formation of coarse-grained Fe3Ge phase rather than nanosized α-Fe grains. The coarse-grained Fe3Ge results in a remarkable drop in magnetic softness.

Fabrication and Properties of Ge-Doped (Bi,Nd)4Ti3O12 Thin Films by Chemical Solution Deposition

Nd- and Ge-codoped Bi4Ti3O12 thin films have been fabricated by chemical solution deposition. The effects of Ge doping in (Bi,Nd)4Ti3O12 on microstructural and ferroelectric properties were investigated for the development of low-temperature fabrication of ferroelectric Bi4Ti3O12-based thin films. Bi3.35Nd0.75Ti3-xGexO12 [0≤x≤0.5] thin films were found to crystallize into the Bi4Ti3O12 phase above 600°C without forming any second phase. The crystal orientation and surface morphology of the synthesized films strongly depended on the Ge content of Bi3.35Nd0.75Ti3-xGexO12. Among various compositions of Bi3.35Nd0.75Ti3-xGexO12, Bi3.35Nd0.75Ti2.9Ge0.1O12 thin films showed excellent surface morphology and ferroelectricity regardless of the processing temperature. Furthermore, the doping of Ge below x=0.1 was found to be effective in improving the ferroelectric properties of the low-temperature-processed films. The Pr values of Bi3.35Nd0.75Ti3-xGexO12 thin films with the optimum Ge content prepared at 600°C were above 15 µC/cm2 and equal to those of the films crystallized at 700°C.

Soft magnetic properties of Ge-doped nanocrystalline Fe–Zr–B alloys

The effects of Ge doping on the coercivity and hyperfine interactions of nanocrystalline Fe 89Zr 7B 3Cu 1 have been investigated by means of DC magnetization measurements and 57Fe Mössbauer spectroscopy. The coercivity of Fe 89− x Zr 7B 3Cu 1Ge x annealed for 3.6 ks at 773 and 823 K exhibits a tendency to decrease with increasing Ge content while this effect is not evident at higher annealing temperatures. Our Mössbauer analysis suggests that Ge-induced magnetic softening in Fe 89− x Zr 7B 3Cu 1Ge x is due to the preferential enrichment of Ge into the residual amorphous phase which results in an enhancement of the exchange stiffness in the intergranular region.