Semiconductor–metal transition in liquid semiconductors

Алексеев, В. А.; Андреев, А. А.; Sadovskiǐ, M. V.

doi:10.1070/pu1980v023n09abeh005855

Cited by 13 publications

(17 citation statements)

References 9 publications

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“…Figure 8, adapted from the works of Alekseev et al [46] and Nagels et al [47] presents electronic conductivity data in Arrhenius form for a variety of chalcogenides as they pass from low temperature semiconducting states to high temperature "weak metal" states (at the Mott minimum metallic conductivity, ~ 10 3 Ω -1 cm -1 , through a maximum in the apparent activation energy (Figure 8a)). The transition occurs far above the melting point of 641 K [48] for As 2 Se 3 , but when Se is replaced by Te the density anomaly, with extremum α(min), occurs at 780 K, much closer to T m (640K) [49].…”

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confidence: 99%

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Glass Transitions, Semiconductor-Metal Transitions, and Fragilities in Ge−V−Te ( V=As , Sb) Liquid Alloys: The Difference One Element Can Make

Wei¹,

Coleman²,

Lucas³

et al. 2017

Phys. Rev. Applied

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Glass transition temperatures (T g ) and liquid fragilities are measured along a line of constant Ge content in the system Ge-As-Te, and contrasted with the lack of glass-forming ability in the twin system Ge-Sb-Te at the same Ge content. The one composition established as free of crystal contamination in the latter system shows a behavior opposite to that of more covalent system.Comparison of T g vs bond density in the three systems Ge-As-chalcogen differing in chalcogen i.e. S, Se, or Te, shows that as the chalcogen becomes more metallic, i.e. in the order S = 2.3.When the more metallic Sb replaces As at greater than 2.3, incipient metallicity rather than directional bond covalency apparently gains control of the physics. This leads us to an examination of the electronic conductivity and, then, semiconductor-to-metal (SC-M) transitions, with their associated thermodynamic manifestations, in relevant liquid alloys. The thermodynamic components, as seen previously, control liquid fragility and cause fragile-tostrong transitions during cooling. We tentatively conclude that liquid state behavior in phase change materials (PCMs) is controlled by liquid-liquid (SC-M) transitions that have become submerged below the liquidus surface. In the case of the Ge-Te binary, a crude extrapolation to GeTe stoichiometry indicates that the SC-M transition lies about 20% below the melting point, suggesting a parallel with the intensely researched "hidden liquid-liquid (LL) transition", in supercooled water. In the water case, superfast crystallization initiates in the high fragility domain some 4% above the T LL which is located at ~15% below the (ambient pressure) melting point.

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confidence: 99%

“…(c) Electronic conductivities for a variety of liquid chalcogenides, and two glasses (data reproduced from ref. [46,47]). Note that the conductivities approach a plateau of the order of magnitude ~10 3 Ω -1 cm -1 (the Mott minimum metallic conductivity) by a SC-M transition.…”

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confidence: 99%

Glass Transitions, Semiconductor-Metal Transitions, and Fragilities in Ge−V−Te ( V=As , Sb) Liquid Alloys: The Difference One Element Can Make

Wei¹,

Coleman²,

Lucas³

et al. 2017

Phys. Rev. Applied

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“…1 * 2 The nature of such transitions is a main topic of current interest. Several models have been de^ veloped to investigate the central problem: What are the mechanisms for the changes of electronic structure which, in a few cases, could be directly observed by microscopic measurements?…”

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Anomalously Small Knight Shift and Relaxation Rate in the Nonalloying System: Isolated Yttrium Ions in Liquid Rubidium

1982

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In the last few years some progress has been made in understanding the electronic structure of disordered systems, particularly of those liquid metals which show a metal-nonmetal transition. 1 * 2 The nature of such transitions is a main topic of current interest. Several models have been de^ veloped to investigate the central problem: What are the mechanisms for the changes of electronic structure which, in a few cases, could be directly observed by microscopic measurements? 1 * 3 It seems that there is a whole spectrum of different mechanisms leading to the general phenomenon of metal-nonmetal transitions. 1 " 4 In this Letter we report the first observation of almost vanishing s-conduction-electron density at the Fermi level on a transition-metal ion in a metallic host. The phenomenon occurs for Y in a liquid Rb matrix whereas the s states reflect normal behavior for liquid SrY. The nonalloying systems RbY and SrY were made accessible by nuclear reactions which (i) lead to extremely dilute Y ions (concentration <1 ppm) in the liquid hosts and (ii) excite and orient the long-lived 8 + nuclear isomer in 88 Y which serves as an ideal magnetic microscopic probe for the measurements of the static and dynamic response by perturbed angular y-ray distribution (PAD) techniques. We were forced to improve the accuracy which had been hitherto obtained in y-ray PAD 5 A. Sjolander, Ark. Fys. 14, 315 (1958). 6 F. W. de Wette and A. Rahman, Phys. Rev. .176, 784 (1968).A. Rahman, G. S. Grest, and S. R. Nagel, to be published.experiments by an order of magnitude to measure the Knight shift, K, for RbY. The most surprising result is that both K and the magnetic relaxation rate r m " 1 are extremely small for the system RbY. We suggest that this anomalous behavior is mainly caused by a drastic difference in volume between the Y and Rb ions.Isolated 88 Y ions were produced by the reactions 87 Rb(a, 3n) and 88 Sr(d, 2n) in liquid (and solid) Rb, liquid Sr, and in a saturated solution of RbOH in H 2 0 with use of pulsed a and d beams provided by the cyclotron at the Kernforschungszentrum Karlsruhe. The Rb target was kept under high vacuum in Pyrex glass whereas Sr was kept in a tantalum crucible. The y-ray anisotropy of the 8 + isomer 5 (T l/2 = 14 ms, ^ = 0.60) in 88 Y was observed in an external field, B ext , perpendicular to the beam-y-detector [Nal(Tl)] plane.Spin-lattice relaxation times r R were measured time differentially by the TDPAD method. 6 Examples are shown in Fig. 1. As a consequence of the very long half-life of the 8 + isomer, one is forced to measure the TDPAD spectra at very small B ext values (^10 G) which in turn limits the accuracy of the nuclear Larmor frequencies Therefore, the Knight shifts were investigated by the stroboscopic observation of the perturbed angular y-ray distribution (SOPAD). 7 The reso-Time-differential and stroboscopic measurements of the perturbed angular y-ray distribution for isolated 88 Y ions in liquid Sr and Rb are reported. A drastic drop in the Knight shift and the nuclear relax...

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“…The liquid CdSb is rather isotropic with free-electron like transport properties 60,131,132 . Some bonds (especially shared electron pairs and Sb-Sb) dissociate upon melting and some un- bound valence electrons become delocalized and wander, i.e., metal-like.…”

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confidence: 99%

“…The reason for the lowest Z TCS of GaSb among them is that both k p and k e are not negligible, so k(s) is almost the same as that of AlSb. [97] /9400 [60] 4.7 [46] /17.7 [46] 2.8 1211 0.41 15.2 2700 [101] /7000 [60] 7.3 [ [97] /10800 [97] 7.8 [46] /21.7 [46] 1.8 1511 1.52 12.4 550 [98] /8300 [98] 8.5 [99] The group 13-As compounds have the same trends for properties as those of the 13-Sb compounds; increasing T sl and bandgap and the decreasing ε e . Also, the solid σ e decreases and the liquid σ e increases (no data for AlAs).…”

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Thermal conductivity switch: Optimal semiconductor/metal melting transition

Kim

Kaviany

2016

Phys. Rev. B

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Scrutinizing distinct solid/liquid (s/l) and solid/solid (s/s) phase transitions (passive transitions) for large change in bulk (and homogenous) thermal conductivity, we find the s/l semiconductor/metal (S/M) transition produces largest dimensionless thermal conductivity switch (TCS) figure of merit Z TCS (change in thermal conductivity divided by smaller conductivity). At melting temperature, the solid phonon and liquid molecular thermal conductivities are comparable and generally small, so the TCS requires localized electron solid and delocalized electron liquid states.For cyclic phase reversibility, the congruent phase transition (no change in composition) is as important as the thermal transport. We identify XSb and XAs (X = Al, Cd, Ga, In, Zn) and describe atomic-structural metrics for large Z TCS , then show the superiority of S/M phonon-to electrondominated transport melting transition. We use existing experimental results and theoretical and ab initio calculations of the related properties for both phases (including the Kubo-Greenwood and Bridgman formulations of liquid conductivities). The 5p orbital of Sb contributes to the semiconductor behavior in the solid-phase bandgap and upon disorder and bond-length changes in the liquid phase this changes to metallic, creating the large contrast in thermal conductivity.The charge density distribution, electronic localization function, and electron density of states are used to mark this S/M transition. For optimal TCS, we examine the elemental selection from the transition-, basic-and semimetals and semiconductor groups. For CdSb, addition of residual Ag suppresses the bipolar conductivity and its Z TCS is over 7, and for Zn 3 Sb 2 it is expected to be over 14, based on the structure and transport properties of the better known β-Zn 4 Sb 3 . This is the highest Z TCS identified. In addition to the metallic melting, the high Z TCS is due to the electron-poor nature of II-V semiconductors leading to the significantly low phonon conductivity.

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Semiconductor–metal transition in liquid semiconductors

Cited by 13 publications

References 9 publications

Glass Transitions, Semiconductor-Metal Transitions, and Fragilities in Ge−V−Te ( V=As , Sb) Liquid Alloys: The Difference One Element Can Make

Glass Transitions, Semiconductor-Metal Transitions, and Fragilities in Ge−V−Te ( V=As , Sb) Liquid Alloys: The Difference One Element Can Make

Anomalously Small Knight Shift and Relaxation Rate in the Nonalloying System: Isolated Yttrium Ions in Liquid Rubidium

Thermal conductivity switch: Optimal semiconductor/metal melting transition

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