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P Rogl - One of the best experts on this subject based on the ideXlab platform.
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caGe forming compounds in the ba rh Ge System from thermoelectrics to superconductivity
Inorganic Chemistry, 2013Co-Authors: Matthias Falmbigl, A Grytsiv, F Kneidinger, M X Chen, H Michor, E Royanian, E Bauer, H Effenberger, R Podloucky, P RoglAbstract:Phase relations and solidification behavior in the Ge-rich part of the phase diagram have been determined in two isothermal sections at 700 and 750 °C and in a liquidus projection. A reaction scheme has been derived in the form of a Schulz−Scheil diagram. Phase equilibria are characterized by three ternary compounds: τ1-BaRhGe3 (BaNiSn3-type) and two novel phases, τ2-Ba3Rh4Ge16 and τ3-Ba5Rh15Ge36‑x, both forming in peritectic reactions. The crystal structures of τ2 and τ3 have been elucidated from single- crystal X-ray intensity data and were found to crystallize in unique structure types: Ba3Rh4Ge16 is tetragonal (I4/mmm, a = 0.65643(2) nm, c = 2.20367(8) nm, and RF = 0.0273), whereas atoms in Ba5Rh15Ge36−x (x = 0.25) arranGe in a larGe orthorhombic unit cell (Fddd, a = 0.84570(2) nm, b = 1.4725(2) nm, c = 6.644(3) nm, and RF = 0.034). The body-centered- cubic superstructure of binary Ba8Ge43□3 was observed to extend at 800 ° Ct o Ba8Rh0.6Ge43□2.4, while the clathrate type I phase, κI-Ba8RhxGe46−x−y□y, reveals a maximum solubility of x = 1.2 Rh atoms in the structure at a vacancy level of y = 2.0. The cubic lattice parameter increases with increasing Rh content. Clathrate I decomposes eutectoidally at 740 °C: κI ⇔ (Ge) + κIX + τ2. A very small solubility ranGe is observed at 750 °C for the clathrate IX, κIX-Ba6RhxGe25−x (x ∼ 0.16). Density functional theory calculations have been performed to derive the enthalpies of formation and densities of states for various compositions Ba8RhxGe46−x (x =0 −6). The physical properties have been investigated for the phases κI, τ1, τ2, and τ3, documenting a chanGe from thermoelectric (κI) to superconducting behavior (τ2). The electrical resistivity of κI-Ba8Rh1.2Ge42.8□2.0 increases almost linearly with the temperature from room temperature to 730 K, and the Seebeck coefficient is negative throughout the same temperature ranGe. τ1-BaRhGe3 has a typical metallic electrical resistivity. A superconducting transition at TC = 6.5 K was observed for τ2-Ba3Rh4Ge16, whereas τ3-Ba5Rh15Ge35.75 showed metallic-like behavior down to 4 K.
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liquidus projection of the ag ba Ge System and melting points of clathrate type i compounds
Journal of Solid State Chemistry, 2012Co-Authors: I Zeiringer, A Grytsiv, Pavel Brož, P RoglAbstract:The liquidus and solidus projection has been constructed for the Ag-Ba-Ge System up to 33.3 at% Ba, using electron micro probe analysis (EPMA), X-ray powder diffraction (XRD) and differential thermal analysis (DSC/DTA). Eight different primary crystallization regions were found: (Ge), Ba{sub 8}Ag{sub x}Ge{sub 46-x-y}{open_square}{sub y} ({kappa}{sub I}) ({open_square} is a vacancy), Ba{sub 6}Ag{sub x}Ge{sub 25-x} ({kappa}{sub Ix}), BaGe{sub 2}, Ba(Ag{sub 1-x}Ge{sub x}){sub 2} ({tau}{sub 1}), BaAg{sub 2-x}Ge{sub 2+x} ({tau}{sub 2}) BaAg{sub 5} and (Ag). The ternary invariant reactions have been determined for the region investigated and are the basis for a Schulz-Scheil diagram. The second part of this work provides a comprehensive compilation of melting points of ternary A{sub 8}T{sub x}M{sub 46-x} and quaternary (A=Sr, Ba, Eu; T=Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga; M=Si, Ge, Sn) clathrate type-I compounds and decomposition temperatures of inverse clathrate type-I Ge{sub 38}{l_brace}P,As,Sb{r_brace}{sub 8}{l_brace}Cl,Br,I{r_brace}{sub 8}, Si{sub 46-x}P{sub x}Te{sub y} and tin based compounds. - Graphical Abstract: Partial liquidus projection of the Ag-Ba-Ge System. Highlights: Black-Right-Pointing-Pointer The liquidus and solidus projection has been constructed for the Ag-Ba-Ge System up to 33.33 at% Ba. Black-Right-Pointing-Pointer Eight different primary crystallization fields have been found. Black-Right-Pointing-Pointer All the ternary compounds form congruently from themore » melt. Black-Right-Pointing-Pointer The ternary invariant reactions have been determined and are the basis for a Schulz-Scheil diagram.« less
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phase equilibria crystal chemistry electronic structure and physical properties of ag ba Ge clathrates
Acta Materialia, 2011Co-Authors: I Zeiringer, A Grytsiv, P Rogl, M X Chen, E Royanian, E Bauer, R Podloucky, Ingeborg Bednar, H EffenbergerAbstract:Abstract In the Ag–Ba–Ge System the clathrate type-Ι solid solution, Ba 8 Ag x Ge 46− x − y □ y , extends at 800 °C from binary Ba 8 Ge 43 □ 3 (□ is a vacancy) to Ba 8 Ag 5.3 Ge 40.7 . For the clathrate phase (1 ⩽ x ⩽ 5.3) the cubic space group Pm 3 ¯ n was established by X-ray powder diffraction and confirmed by X-ray single-crystal analyses of the samples Ba 8 Ag 2.3 Ge 41.9 □ 1.8 and Ba 8 Ag 4.4 Ge 41.3 □ 0.3 . Increasing the concentration of Ag causes the lattice parameters of the solid solution to increase linearly from a value of a = 1.0656 ( x = 0, y = 3) to a = 1.0842 ( x = 4.8, y = 0) nm. Site preference determination using X-ray refinement reveals that Ag atoms preferentially occupy the 6d site randomly mixed with Ge and vacancies, which become filled in the compound Ba 8 Ag 4.8 Ge 41.2 when the Ag content increases. At 600 °C the phase region of the clathrate solution Ba 8 Ag x Ge 46− x − y □ y becomes separated from the Ba–Ge boundary and extends from 6.6 to 9.8 at.% Ag. The compound Ba 6 Ge 25 (clathrate type-ΙX) dissolves at 800 °C a maximum of 1.5 at.% Ag. The homoGeneity regions of the two ternary compounds BaAg 2− x Ge 2+ x (ThCr 2 Si 2 -type, 0.2 ⩽ x ⩽ 0.7) and Ba(Ag 1 -x Ge x ) 2 (AlB 2 -type, 0.65 ⩽ x ⩽ 0.75) were established at 800 °C. Studies of transport properties for the series of Ba 8 Ag x Ge 46− x − y □ y compounds evidenced that electrons are the predominant charGe carriers with the Fermi energy close to a gap. Its position can be fine-tuned by the substitution of Ge by Ag atoms and by mechanical processing of the starting material, Ba 8 Ge 43 . The proximity of the electronic structure at Fermi energy of Ba 8 Ag x Ge 46− x − y □ y to a gap is also corroborated by density functional theory calculations. This gap near the Fermi energy gives rise to distinct features of the temperature-dependent electrical resistivity and the Seebeck effect is in very good agreement with the experiment findings.
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crystal structure and physical properties of quaternary clathrates ba8znxGe46 x ysiy ba8 zn cu xGe46 x and ba8 zn pd xGe46 x
Journal of Solid State Chemistry, 2010Co-Authors: Navida Nasir, A Grytsiv, P Rogl, Nataliya Melnychenkokoblyuk, Ingeborg Bednar, E BauerAbstract:Abstract Three series of vacancy-free quaternary clathrates of type I, Ba 8 Zn x Ge 46− x − y Si y , Ba 8 (Zn,Cu) x Ge 46− x , and Ba 8 (Zn,Pd) x Ge 46− x , have been prepared by reactions of elemental ingots in vacuum sealed quartz at 800 °C. In all cases cubic primitive symmetry (space group Pm 3 n , a ∼1.1 nm) was confirmed for the clathrate phase by X-ray powder diffraction and X-ray single crystal analyses. The lattice parameters show a linear increase with increase in Ge for Ba 8 Zn x Ge 46− x − y Si y . M atoms (Zn, Pd, Cu) preferably occupy the 6 d site in random mixtures. No defects were observed for the 6 d site. Site preference of Ge and Si in Ba 8 Zn x Ge 46− x − y Si y has been elucidated from X-ray refinement: Ge atoms linearly substitute Si in the 24 k site whilst a significant deviation from linearity is observed for occupation of the 16 i site. A connectivity scheme for the phase equilibria in the “Ba 8 Ge 46 ” corner at 800 °C has been derived and a three-dimensional isothermal section at 800 °C is presented for the Ba–Pd–Zn–Ge System. Studies of transport properties carried out for Ba 8 {Cu,Pd,Zn} x Ge 46− x and Ba 8 Zn x Si y Ge 46− x − y evidenced predominantly electrons as charGe carriers and the closeness of the Systems to a metal-to-insulator transition, fine-tuned by substitution and mechanical processing of starting material Ba 8 Ge 43 . A promising figure of merit, ZT ∼0.45 at 750 K, has been derived for Ba 8 Zn 7.4 Ge 19.8 Si 18.8 , where pricey Germanium is exchanGed by reasonably cheap silicon.
Ryoji Kanno - One of the best experts on this subject based on the ideXlab platform.
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synthesis structure and lithium ionic conductivity of solid solutions of li 10 Ge 1 x m x p 2 s 12 m si sn
Journal of Power Sources, 2014Co-Authors: Masaaki Hirayama, Yuki Kato, Ryoko Saito, Mitsuru Sakano, Akio Mitsui, Ryoji KannoAbstract:Abstract The mixed cation System, Li 10 (Ge 1− x M x )P 2 S 12 (M = Si, Sn), was synthesized and the ionic conductivities of the resulting solid solutions were determined. The Si–Ge and Ge–Sn Systems provided single phase solid solutions for the composition 0 ≤ x x ≤ 1.0 in Li 10 (Ge 1− x Si x )P 2 S 12 and Li 10 (Ge 1− x Sn x )P 2 S 12 , respectively. The lattice size gradually increased from Si to Sn through the Ge Systems, reflecting the ionic size of these elements. On the other hand, conductivity did not follow the increase in lattice volume. Conductivity increased in the Si to Ge System, with the maximum conductivity value of 8.6 × 10 −3 S cm −1 provided by the compressed powder with the composition Li 10 Ge 0.95 Si 0.05 P 2 S 12 , which is close to the original Li 10 GeP 2 S 12 (LGPS) composition. The conductivity decreased with increasing Sn content, indicating that lattice volume is not the only parameter that affects ionic conduction in this structure. The relationship between conductivity and lattice volume is discussed.
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synthesis structure and lithium ionic conductivity of solid solutions of li10 Ge1 xmx p2s12 m si sn
Journal of Power Sources, 2014Co-Authors: Masaaki Hirayama, Yuki Kato, Ryoko Saito, Mitsuru Sakano, Akio Mitsui, Ryoji KannoAbstract:Abstract The mixed cation System, Li 10 (Ge 1− x M x )P 2 S 12 (M = Si, Sn), was synthesized and the ionic conductivities of the resulting solid solutions were determined. The Si–Ge and Ge–Sn Systems provided single phase solid solutions for the composition 0 ≤ x x ≤ 1.0 in Li 10 (Ge 1− x Si x )P 2 S 12 and Li 10 (Ge 1− x Sn x )P 2 S 12 , respectively. The lattice size gradually increased from Si to Sn through the Ge Systems, reflecting the ionic size of these elements. On the other hand, conductivity did not follow the increase in lattice volume. Conductivity increased in the Si to Ge System, with the maximum conductivity value of 8.6 × 10 −3 S cm −1 provided by the compressed powder with the composition Li 10 Ge 0.95 Si 0.05 P 2 S 12 , which is close to the original Li 10 GeP 2 S 12 (LGPS) composition. The conductivity decreased with increasing Sn content, indicating that lattice volume is not the only parameter that affects ionic conduction in this structure. The relationship between conductivity and lattice volume is discussed.
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synthesis structure and ionic conductivity of solid solution li10 δm1 δp2 δs12 m si sn
Faraday Discussions, 2014Co-Authors: Satoshi Hori, Kota Suzuki, Masaaki Hirayama, Yuki Kato, Toshiya Saito, Masao Yonemura, Ryoji KannoAbstract:Solid solutions of the silicon and tin analogous phases of the superionic conductor Li10MP2S12 (M = Si, Sn) were synthesized by a conventional solid-state reaction in an evacuated silica tube at 823 K. The ranGes of the solid solutions were determined to be 0.20 < δ < 0.43 and −0.25 < δ < −0.01 in Li10+δM1+δP2−δS12 (0.525 ≤ k ≤ 0.60 and 0.67 ≤ k ≤ 0.75 in Li4−kM1−kPkS4) for the Si and Sn Systems, respectively. The ionic conductivity of these Systems varied as a function of the changing M ions: the Si and Sn Systems showed lower conductivity than the Ge System, Li10+δGe1+δP2−δS12. The conductivity chanGe for different elements might be due to the lattice size and lithium content affecting the ionic conduction. The relationship between ionic conduction, structure, and lithium concentration is discussed based on the structural and electrochemical information for the silicon, Germanium, and tin Systems.
Yuki Kato - One of the best experts on this subject based on the ideXlab platform.
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synthesis structure and lithium ionic conductivity of solid solutions of li 10 Ge 1 x m x p 2 s 12 m si sn
Journal of Power Sources, 2014Co-Authors: Masaaki Hirayama, Yuki Kato, Ryoko Saito, Mitsuru Sakano, Akio Mitsui, Ryoji KannoAbstract:Abstract The mixed cation System, Li 10 (Ge 1− x M x )P 2 S 12 (M = Si, Sn), was synthesized and the ionic conductivities of the resulting solid solutions were determined. The Si–Ge and Ge–Sn Systems provided single phase solid solutions for the composition 0 ≤ x x ≤ 1.0 in Li 10 (Ge 1− x Si x )P 2 S 12 and Li 10 (Ge 1− x Sn x )P 2 S 12 , respectively. The lattice size gradually increased from Si to Sn through the Ge Systems, reflecting the ionic size of these elements. On the other hand, conductivity did not follow the increase in lattice volume. Conductivity increased in the Si to Ge System, with the maximum conductivity value of 8.6 × 10 −3 S cm −1 provided by the compressed powder with the composition Li 10 Ge 0.95 Si 0.05 P 2 S 12 , which is close to the original Li 10 GeP 2 S 12 (LGPS) composition. The conductivity decreased with increasing Sn content, indicating that lattice volume is not the only parameter that affects ionic conduction in this structure. The relationship between conductivity and lattice volume is discussed.
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synthesis structure and lithium ionic conductivity of solid solutions of li10 Ge1 xmx p2s12 m si sn
Journal of Power Sources, 2014Co-Authors: Masaaki Hirayama, Yuki Kato, Ryoko Saito, Mitsuru Sakano, Akio Mitsui, Ryoji KannoAbstract:Abstract The mixed cation System, Li 10 (Ge 1− x M x )P 2 S 12 (M = Si, Sn), was synthesized and the ionic conductivities of the resulting solid solutions were determined. The Si–Ge and Ge–Sn Systems provided single phase solid solutions for the composition 0 ≤ x x ≤ 1.0 in Li 10 (Ge 1− x Si x )P 2 S 12 and Li 10 (Ge 1− x Sn x )P 2 S 12 , respectively. The lattice size gradually increased from Si to Sn through the Ge Systems, reflecting the ionic size of these elements. On the other hand, conductivity did not follow the increase in lattice volume. Conductivity increased in the Si to Ge System, with the maximum conductivity value of 8.6 × 10 −3 S cm −1 provided by the compressed powder with the composition Li 10 Ge 0.95 Si 0.05 P 2 S 12 , which is close to the original Li 10 GeP 2 S 12 (LGPS) composition. The conductivity decreased with increasing Sn content, indicating that lattice volume is not the only parameter that affects ionic conduction in this structure. The relationship between conductivity and lattice volume is discussed.
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synthesis structure and ionic conductivity of solid solution li10 δm1 δp2 δs12 m si sn
Faraday Discussions, 2014Co-Authors: Satoshi Hori, Kota Suzuki, Masaaki Hirayama, Yuki Kato, Toshiya Saito, Masao Yonemura, Ryoji KannoAbstract:Solid solutions of the silicon and tin analogous phases of the superionic conductor Li10MP2S12 (M = Si, Sn) were synthesized by a conventional solid-state reaction in an evacuated silica tube at 823 K. The ranGes of the solid solutions were determined to be 0.20 < δ < 0.43 and −0.25 < δ < −0.01 in Li10+δM1+δP2−δS12 (0.525 ≤ k ≤ 0.60 and 0.67 ≤ k ≤ 0.75 in Li4−kM1−kPkS4) for the Si and Sn Systems, respectively. The ionic conductivity of these Systems varied as a function of the changing M ions: the Si and Sn Systems showed lower conductivity than the Ge System, Li10+δGe1+δP2−δS12. The conductivity chanGe for different elements might be due to the lattice size and lithium content affecting the ionic conduction. The relationship between ionic conduction, structure, and lithium concentration is discussed based on the structural and electrochemical information for the silicon, Germanium, and tin Systems.
Shashank Priya - One of the best experts on this subject based on the ideXlab platform.
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quasi zero lattice mismatch and band alignment of batio3 on epitaxial 110 Ge
Journal of Applied Physics, 2013Co-Authors: Mantu K Hudait, Yizheng Zhu, Nikhil Jain, Deepam Maurya, Ying Zhou, Shashank PriyaAbstract:Growth, structural, and band alignment properties of pulsed laser deposited amorphous BaTiO3 on epitaxial molecular beam epitaxy grown (110)Ge layer, as well as their utilization in low power transistor are reported. High-resolution x-ray diffraction demonstrated quasi-zero lattice mismatch of BaTiO3 on (110)Ge. Cross-sectional transmission electron microscopy micrograph confirms the amorphous nature of BaTiO3 layer as well as shows a sharp heterointerface between BaTiO3 and Ge with no traceable interfacial layer. The valence band offset, ΔEv, of 1.99 ± 0.05 eV at the BaTiO3/(110)Ge heterointerface is measured using x-ray photoelectron spectroscopy. The conduction band offset, ΔEc, of 1.14 ± 0.1 eV is calculated using the bandgap energies of BaTiO3 of 3.8 eV and Ge of 0.67 eV. These band offset parameters for carrier confinement and the interface chemical properties of the BaTiO3/(110)Ge System are significant advancement towards designing Ge-based p-and n-channel metal-oxide semiconductor field-effect transistors for low-power application.
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energy band alignment of atomic layer deposited hfo2 on epitaxial 110 Ge grown by molecular beam epitaxy
Applied Physics Letters, 2013Co-Authors: Mantu K Hudait, Deepam Maurya, Shashank PriyaAbstract:The band alignment properties of atomic layer HfO2 film deposited on epitaxial (110)Ge, grown by molecular beam epitaxy, was investigated using x-ray photoelectron spectroscopy. The cross-sectional transmission electron microscopy exhibited a sharp interface between the (110)Ge epilayer and the HfO2 film. The measured valence band offset value of HfO2 relative to (110)Ge was 2.28 ± 0.05 eV. The extracted conduction band offset value was 2.66 ± 0.1 eV using the bandgaps of HfO2 of 5.61 eV and Ge bandgap of 0.67 eV. These band offset parameters and the interface chemical properties of HfO2/(110)Ge System are of tremendous importance for the design of future high hole mobility and low-power Ge-based metal-oxide transistor devices.
A Grytsiv - One of the best experts on this subject based on the ideXlab platform.
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caGe forming compounds in the ba rh Ge System from thermoelectrics to superconductivity
Inorganic Chemistry, 2013Co-Authors: Matthias Falmbigl, A Grytsiv, F Kneidinger, M X Chen, H Michor, E Royanian, E Bauer, H Effenberger, R Podloucky, P RoglAbstract:Phase relations and solidification behavior in the Ge-rich part of the phase diagram have been determined in two isothermal sections at 700 and 750 °C and in a liquidus projection. A reaction scheme has been derived in the form of a Schulz−Scheil diagram. Phase equilibria are characterized by three ternary compounds: τ1-BaRhGe3 (BaNiSn3-type) and two novel phases, τ2-Ba3Rh4Ge16 and τ3-Ba5Rh15Ge36‑x, both forming in peritectic reactions. The crystal structures of τ2 and τ3 have been elucidated from single- crystal X-ray intensity data and were found to crystallize in unique structure types: Ba3Rh4Ge16 is tetragonal (I4/mmm, a = 0.65643(2) nm, c = 2.20367(8) nm, and RF = 0.0273), whereas atoms in Ba5Rh15Ge36−x (x = 0.25) arranGe in a larGe orthorhombic unit cell (Fddd, a = 0.84570(2) nm, b = 1.4725(2) nm, c = 6.644(3) nm, and RF = 0.034). The body-centered- cubic superstructure of binary Ba8Ge43□3 was observed to extend at 800 ° Ct o Ba8Rh0.6Ge43□2.4, while the clathrate type I phase, κI-Ba8RhxGe46−x−y□y, reveals a maximum solubility of x = 1.2 Rh atoms in the structure at a vacancy level of y = 2.0. The cubic lattice parameter increases with increasing Rh content. Clathrate I decomposes eutectoidally at 740 °C: κI ⇔ (Ge) + κIX + τ2. A very small solubility ranGe is observed at 750 °C for the clathrate IX, κIX-Ba6RhxGe25−x (x ∼ 0.16). Density functional theory calculations have been performed to derive the enthalpies of formation and densities of states for various compositions Ba8RhxGe46−x (x =0 −6). The physical properties have been investigated for the phases κI, τ1, τ2, and τ3, documenting a chanGe from thermoelectric (κI) to superconducting behavior (τ2). The electrical resistivity of κI-Ba8Rh1.2Ge42.8□2.0 increases almost linearly with the temperature from room temperature to 730 K, and the Seebeck coefficient is negative throughout the same temperature ranGe. τ1-BaRhGe3 has a typical metallic electrical resistivity. A superconducting transition at TC = 6.5 K was observed for τ2-Ba3Rh4Ge16, whereas τ3-Ba5Rh15Ge35.75 showed metallic-like behavior down to 4 K.
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liquidus projection of the ag ba Ge System and melting points of clathrate type i compounds
Journal of Solid State Chemistry, 2012Co-Authors: I Zeiringer, A Grytsiv, Pavel Brož, P RoglAbstract:The liquidus and solidus projection has been constructed for the Ag-Ba-Ge System up to 33.3 at% Ba, using electron micro probe analysis (EPMA), X-ray powder diffraction (XRD) and differential thermal analysis (DSC/DTA). Eight different primary crystallization regions were found: (Ge), Ba{sub 8}Ag{sub x}Ge{sub 46-x-y}{open_square}{sub y} ({kappa}{sub I}) ({open_square} is a vacancy), Ba{sub 6}Ag{sub x}Ge{sub 25-x} ({kappa}{sub Ix}), BaGe{sub 2}, Ba(Ag{sub 1-x}Ge{sub x}){sub 2} ({tau}{sub 1}), BaAg{sub 2-x}Ge{sub 2+x} ({tau}{sub 2}) BaAg{sub 5} and (Ag). The ternary invariant reactions have been determined for the region investigated and are the basis for a Schulz-Scheil diagram. The second part of this work provides a comprehensive compilation of melting points of ternary A{sub 8}T{sub x}M{sub 46-x} and quaternary (A=Sr, Ba, Eu; T=Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga; M=Si, Ge, Sn) clathrate type-I compounds and decomposition temperatures of inverse clathrate type-I Ge{sub 38}{l_brace}P,As,Sb{r_brace}{sub 8}{l_brace}Cl,Br,I{r_brace}{sub 8}, Si{sub 46-x}P{sub x}Te{sub y} and tin based compounds. - Graphical Abstract: Partial liquidus projection of the Ag-Ba-Ge System. Highlights: Black-Right-Pointing-Pointer The liquidus and solidus projection has been constructed for the Ag-Ba-Ge System up to 33.33 at% Ba. Black-Right-Pointing-Pointer Eight different primary crystallization fields have been found. Black-Right-Pointing-Pointer All the ternary compounds form congruently from themore » melt. Black-Right-Pointing-Pointer The ternary invariant reactions have been determined and are the basis for a Schulz-Scheil diagram.« less
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phase equilibria crystal chemistry electronic structure and physical properties of ag ba Ge clathrates
Acta Materialia, 2011Co-Authors: I Zeiringer, A Grytsiv, P Rogl, M X Chen, E Royanian, E Bauer, R Podloucky, Ingeborg Bednar, H EffenbergerAbstract:Abstract In the Ag–Ba–Ge System the clathrate type-Ι solid solution, Ba 8 Ag x Ge 46− x − y □ y , extends at 800 °C from binary Ba 8 Ge 43 □ 3 (□ is a vacancy) to Ba 8 Ag 5.3 Ge 40.7 . For the clathrate phase (1 ⩽ x ⩽ 5.3) the cubic space group Pm 3 ¯ n was established by X-ray powder diffraction and confirmed by X-ray single-crystal analyses of the samples Ba 8 Ag 2.3 Ge 41.9 □ 1.8 and Ba 8 Ag 4.4 Ge 41.3 □ 0.3 . Increasing the concentration of Ag causes the lattice parameters of the solid solution to increase linearly from a value of a = 1.0656 ( x = 0, y = 3) to a = 1.0842 ( x = 4.8, y = 0) nm. Site preference determination using X-ray refinement reveals that Ag atoms preferentially occupy the 6d site randomly mixed with Ge and vacancies, which become filled in the compound Ba 8 Ag 4.8 Ge 41.2 when the Ag content increases. At 600 °C the phase region of the clathrate solution Ba 8 Ag x Ge 46− x − y □ y becomes separated from the Ba–Ge boundary and extends from 6.6 to 9.8 at.% Ag. The compound Ba 6 Ge 25 (clathrate type-ΙX) dissolves at 800 °C a maximum of 1.5 at.% Ag. The homoGeneity regions of the two ternary compounds BaAg 2− x Ge 2+ x (ThCr 2 Si 2 -type, 0.2 ⩽ x ⩽ 0.7) and Ba(Ag 1 -x Ge x ) 2 (AlB 2 -type, 0.65 ⩽ x ⩽ 0.75) were established at 800 °C. Studies of transport properties for the series of Ba 8 Ag x Ge 46− x − y □ y compounds evidenced that electrons are the predominant charGe carriers with the Fermi energy close to a gap. Its position can be fine-tuned by the substitution of Ge by Ag atoms and by mechanical processing of the starting material, Ba 8 Ge 43 . The proximity of the electronic structure at Fermi energy of Ba 8 Ag x Ge 46− x − y □ y to a gap is also corroborated by density functional theory calculations. This gap near the Fermi energy gives rise to distinct features of the temperature-dependent electrical resistivity and the Seebeck effect is in very good agreement with the experiment findings.
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crystal structure and physical properties of quaternary clathrates ba8znxGe46 x ysiy ba8 zn cu xGe46 x and ba8 zn pd xGe46 x
Journal of Solid State Chemistry, 2010Co-Authors: Navida Nasir, A Grytsiv, P Rogl, Nataliya Melnychenkokoblyuk, Ingeborg Bednar, E BauerAbstract:Abstract Three series of vacancy-free quaternary clathrates of type I, Ba 8 Zn x Ge 46− x − y Si y , Ba 8 (Zn,Cu) x Ge 46− x , and Ba 8 (Zn,Pd) x Ge 46− x , have been prepared by reactions of elemental ingots in vacuum sealed quartz at 800 °C. In all cases cubic primitive symmetry (space group Pm 3 n , a ∼1.1 nm) was confirmed for the clathrate phase by X-ray powder diffraction and X-ray single crystal analyses. The lattice parameters show a linear increase with increase in Ge for Ba 8 Zn x Ge 46− x − y Si y . M atoms (Zn, Pd, Cu) preferably occupy the 6 d site in random mixtures. No defects were observed for the 6 d site. Site preference of Ge and Si in Ba 8 Zn x Ge 46− x − y Si y has been elucidated from X-ray refinement: Ge atoms linearly substitute Si in the 24 k site whilst a significant deviation from linearity is observed for occupation of the 16 i site. A connectivity scheme for the phase equilibria in the “Ba 8 Ge 46 ” corner at 800 °C has been derived and a three-dimensional isothermal section at 800 °C is presented for the Ba–Pd–Zn–Ge System. Studies of transport properties carried out for Ba 8 {Cu,Pd,Zn} x Ge 46− x and Ba 8 Zn x Si y Ge 46− x − y evidenced predominantly electrons as charGe carriers and the closeness of the Systems to a metal-to-insulator transition, fine-tuned by substitution and mechanical processing of starting material Ba 8 Ge 43 . A promising figure of merit, ZT ∼0.45 at 750 K, has been derived for Ba 8 Zn 7.4 Ge 19.8 Si 18.8 , where pricey Germanium is exchanGed by reasonably cheap silicon.
