Liquid Tl Research Articles

The electronic properties and structure of liquid Tl-Se and Ga-Se alloys

Liquid alloys of the group (III) elements (Ga, In and Tl) and the group (VI) elements (S, Se and Te) show a diverse range of behaviour. It is presumed that these properties arise due to the two possible valence states of the group (III) element and the tendency for the chalcogenide element to form pairs in the liquid state. In this paper results are presented showing that liquid Ga x Se 1 − x remains semiconducting with σ < ~ 20 Ω −1 cm −1 for all compositions between 0.4 < x < 0.5 but becomes progressively more metallic for x > 0.5. In contrast liquid Tl x Se 1 − x remains a good semiconductor for all compositions up to x = 0.67 and then becomes more metallic. Using recent neutron diffraction data, it is demonstrated that the low conductivity of Tl-Se alloys is fully explained in terms of an ionic type semiconductor where the conductivity remains low due to the formation of charged Se 2 pairs in the liquid for x < 0.67. On the other hand, the semiconducting alloys of liquid Ga-Se are shown to be characterised as a low density tetrahedrally coordinated covalent type structure reminiscent of the solid state structures in which Ga-Ga bonding is known to occur. These results give strong clues in understanding the particularly unusual properties of liquid In-Se alloys.

Radial Distribution Studies of Tl-S Alloys in Liquid and Amorphous States

Neutron diffraction measurements in liquid Tl x S 1- x alloys with x =0.67, 0.57, 0.50, 0.33 and 0.29 have been carried out to obtain their short-range structures. For the comparison, the amorphous structure of the alloys with 0.50 ≥ x ≥0.29 has been investigated also through X-ray diffraction measurements. The liquid alloy has a chemical order relating to the crystalline phase at x =0.67 (corresponding to the composition of Tl 2 S), where the metal-nonmetal transition occurs. The liquid structure at the rest four compositions is considerably different from the corresponding crystalline one. Consequently, two distinct chemical orders appear in the composition range between Tl 2 S and S in the liquid state, i.e., the Tl 2 S-like chemical order and sulfur linkage unit. On the other hand, crystalline chemical orders are rather retained in the amorphous state, for example, TlS 4/2 tetrahedra in crystalline TlS and Tl 2 S 5 molecular units in crystalline Tl 2 S 5 have been observed also in the amorphous state.

Inelastic Light Scattering in Zinc Germanium Diphosphide Crystals

ABSTRACTThe inelastic light scattering spectra of chalcopyrite structure ZnGeP2 crystals grown by an improved low temperature crystallization from the nonstoichiometric solution of this compound in the liquid Bi or liquid Tl solutions as well as grown by high temperature Bridgman technique has been investigated together with the optical absorption and electron transport measurements.

The Compound-Forming Behaviour in Liquid (Tl1/2Pb1/2)–Te and (In1/2Pb1/2)–Te Systems

The electrical conductivity, magnetic susceptibility and thermoelectric power of liquid (Tl 1/2 Pb 1/2 )–Te and (In 1/2 Pb 1/2 )–Te systems have been measured as a function of composition in the temperature range from near the melting point to 1000° C. The former system exhibits a conductivity minimum, diamagnetic maximum and change in the sign of thermoelectric power in the vicinity of 42.8 at.%Te (corresponding to the stoichiometric composition of Tl 2 Pb 2 Te 3 ). On the other hand, similar anomalies of electronic properties have been observed around 55.6 at.%Te (the stoichiometric composition of In 2 Pb 2 Te 5 ) in the latter In system. In addition, the temperature dependence of these electronic properties considerably differs in both systems, reflecting the bonding nature of Tl–Te or In–Te pair. Energy band parameters around the Fermi level at the stoichiometric composition in both systems have been determined based on the model recently developed by Enderby and Barnes (Rep. Prog. Phys. 53 (1990) 85).

Neutron diffraction study of liquid (Tl 1/2Pb 1/2)−X(X:Te, Se) systems

Neutron diffraction measurements have been carried out on liquid (Tl 1/2 Pb 1/2) 1− y X y (X:Te,Se) systems which exhibit a typical compound-forming behaviour at y = 3 7 . Radial distribution analysis at y = 3 7 has indicated that the bonding nature of Tl X and Pb X is more or less ionic, as expected from the previous result of electronic properties. In order to investigate the difference in electronic behaviour between these two liquid systems in the chalcogen rich region, we derive the X—X partial distribution function g X−X( r, assuming that each partial function at y > 3 7 is independent of the alloy composition. g Se−Se( r) has a well-resolved first peak at r ∼ 0.230 nm, suggesting that covalent Se Se bonds appear in the Se rich region. On the other hand, g Te−Te( r) is somewhat structureless, although the first peak is included in the covalent region. The whole functional form of both g X−X( r) is roughly similar to that of g ( r) in pure liquid Te or Se.

Electronic and Structural Properties of the Liquid (Tl1/2Pb1/2)‐Se System

AbstractThe electrical conductivity, magnetic susceptibility, and thermoelectric power in the liquid (Tl1/2Pb1/2) Se system are measured over wide temperature and composition ranges. It is observed that the electrical conductivity in the system sharply falls near the stoichiometric composition of Tl2Pb2Se3 and the magnetic susceptibility has a diamagnetic maximum at this composition, where the thermoelectric power changes its sign. In addition, the DTA investigation shows that the liquidus temperature of the system has a maximum around this composition. These results suggest that a short‐range order appears around the composition of Tl2Pb2Se3 in the liquid (Tl1/2Pb1/2)‐Se system. The delocalized electron analysis using both susceptibility and conductivity data suggests that the bonding nature of liquid Ti2Pb2Se3 is rather ionic. The radial distribution study by neutron diffraction also exhibits that the first peak position of g(r) for liquid Tl2Pb2Se3 is located near the ionic bond distance of metal and chalcogen atoms. On the other hand, covalent Se‐ Se bonds are formed in the Se‐rich composition range.

Molar Volume and Compressibilityof Liquid Tl–Se Alloys

Molar volume and sound velocity have been measured as a function of temperature in liquid Tl–Se alloys. Above the upper critical solution temperature for the two-melt phase separation between Tl and Tl 2 Se, the critical behaviour of the sound velocity has been observed as the critical temperature is approached. The sound velocity has been used to deduce the compressibility. The molar volume and compressibility have been found to have a cusp-like local maximum at Tl 2 Se. The results suggest the existence of the stable ionic Tl 2 Se association in the liquid.

Electronic properties of liquid alkali-thallium alloys

Measurements of the electrical resistivity, π, and the magnetic susceptibility, χ M, of liquid RbTl and CsTl alloys are reported. The resistivity shows a maximum value of about 610 μΩ cm at 50 at.% Rb on its isotherm. At this concentration, the temperature coefficient of ϱ has a sharp minimum. In addition, at this alkali concentration, the negative deviations of χ M from the linear law are large for liquid RbTl and CsTl. Formation of Zintl ions of sp 3 diamond lattice type may be responsible for these large localization tendencies.

Electronic and ionic conductions in molten Tl-chalcogen systems

Electronic and ionic conductivities of liquid TlSe alloys have been measured separately as a function of concentration and temperature. The system shows a deep minimum in the electronic conductivity at the stoichiometric composition (Tl 2Se). An anomaly in the dependence of the ionic conductivity on the composition has been observed around the composition Tl 2Se. A very unusual negative temperature dependence of the ionic conductivity has been confirmed in the Tl-rich range beyond the composition Tl 2Se.

Sound velocity in the liquid TlSe system

To investigate the thermodynamic properties of the liquid TlSe system, which has two immiscible regions, one at the Tl-rich side and the other at the Se-rich side, the sound velocity and density have been measured over the entire composition range. Above the upper critical solution temperature for the two-melt phase separation between Tl and Tl 2Se, critical behaviour of the sound velocity is observed as the critical temperature is approached. A similar phenomenon could not be observed for the phase separation at the Se-rich side, however. The sound velocity has been used to deduce the adiabatic compressibility which has been found to have a cusp-like maximum at Tl 2Se. The results suggest the existence of the stable ionic Tl 2Se association in the liquid.

Thermodynamics of the volatilization of thallium(I) oxide from Tl2O, Tl4O3, and Tl2O3

Volatile thallous oxide, Tl[sub 2]O, is used in the fabrication of thallium-containing high-temperature superconducting powders and films. The partial pressure of thallous oxide was measured as a function of temperature and oxygen partial pressure by the transportation method over liquid and solid Tl[sub 2]O, liquid and solid Tl[sub 4]O[sub 3], and solid Tl[sub 2]O[sub 3]. At low oxygen partial pressure, condensed Tl[sub 2]O is stable with respect to Tl[sub 4]O[sub 3] and Tl[sub 2]O[sub 3]. It melts at 852 [+-] 10 K and is very volatile, with a vapor pressure of about 1.0 [times] 10[sup [minus]2] atm at 900 K. At high oxygen partial pressure, Tl[sub 2]O[sub 3] is stable with respect to Tl[sub 2]O and Tl[sub 4]O[sub 3]. It does not melt congruently below 1,067 K. It volatilizes congruently through the reaction Tl[sub 2]O[sub 3](c) = Tl[sub 2]O(g) + O[sub 2](g), and the equilibrium vapor pressure of Tl[sub 2]O in oxygen at atmospheric pressure reaches 1.0 [times] 10[sup [minus]2] atm at about 1,050 K. Tl[sub 4]O[sub 3] exists as a thermodynamically stable phase at intermediate oxygen partial pressure. It melts at 990 [+-] 2 K, and it volatilizes congruently through the reaction Tl[sub 4]O[sub 3](c) = 2 Tl[sub 2]O(g)more » + 1/2O[sub 2](g). Thermodynamic properties for Tl[sub 4]O[sub 3](c) are estimated to be [Delta][sub f]H[degrees][sub 298] = [minus]520.7 kJ/mol and S[degrees][sub 298] = 259.0 J/(mol K). The experimental results of this study were combined with data in previous studies to estimate the high temperature thermodynamic properties of the thallium oxide phases. These properties were used to generate a phase diagram for the Tl-O system and to determine the equilibrium vapor pressure of thallous oxide over the condensed phases as a function of temperature and oxygen partial pressure. 30 refs., 10 figs., 3 tabs.« less

Electronic and Ionic Conductions in Liquid Tl–Se Alloys

Electronic and ionic conductivities of liquid Tl–Se alloys have separately been measured as a function of concentration and temperature. The system shows a deep minimum in the electronic conductivity at the stoichiometric composition (Tl 2 Se). A characteristic decay time which is calculated from the slope of the potential decay is found to decrease with temperature for the liquid Tl 2 Se. An anomaly in the ionic conductivity around the composition Tl 2 Se has been observed. A very unusual negative temperature dependence of the ionic conductivity has been confirmed at Tl-rich range beyond the composition Tl 2 Se.

Neutron Diffraction Study of Liquid Tl–Se Alloys

A neutron diffraction study on the liquid Tl–Se system has been carried out over the whole concentration range. Profiles of the total structure factors or the pair distribution functions are essentially similar to those of pure liquid Tl up to 66.7 at.% Tl content, suggesting that there forms a certain short range order in the liquid state which is not far from the structure in the sense of short range scale of the pure liquid Tl. The existence of covalent-type Se polymeric structure is confirmed in Se-rich composition range. We have also derived the partial structure factors, using three different total structure factors in a small concentration range, where the partial structure factors were assumed to be constant.

Heat Capacity of Liquid Tl-Te Alloys

The measurements of heat capacity were made for liquid Tl-Te alloys using an adiabatic scanning calorimeter over the whole concentration range. The excess heat capacity for liquid Te-rich Tl-Te alloys can be attributed to the change in the bonding configuration around Te. The concentration dependence of the heat capacity suggests that the bonding nature changes gradually with increasing Tl content and drastically changes around the composition of Tl 2 Te. The heat capacity for liquid Tl 2 Te alloys has a small temperature coefficient at temperature where a nonmetal-metal transition occurs. It means that the excess heat capacity for liquid Tl 2 Te alloy may not be due to the dissociation of the chemical complex.

Structural study of liquid NaTl alloys by neutron diffraction

Neutron diffraction investigation of liquid NaTl alloys has been carried out to reveal the short range order in the liquid state. In the Na-rich region, an additional small peak has been clearly observed in the low Q side of the main peak and this implies the formation of a local atomic association or a short range order in this alloy system and such short range ordering has also been discussed in comparison with the atomic configuration of the solid NaTl phase.

X-ray and neutron diffraction studies of liquid TlSe system

The composition dependence of the structure for liquid Tl xSe 1−x (x=0.4, 0.5 and 0.667) was investigated by means of X-ray and TOF neutron diffractions. The difference in experimental total structure factors from both radiations was used to infer the feature of partial structural functions for each composition. A significant structural change was found between these compositions. The nearest neighbour peak at r=2.4 A ̊ in the SeSe distribution function observed at x=0.4 and 0.5 , agrees well with that in pure liquid Se, indicating the existence of SeSe chains at these compositions. On the other hand, this SeSe peak disappears at x=0.667. The liquid structure at this composition may be considered to have a short-range order characteristic of the crystalline Tl 2Se.

Structure and electronic properties of liquid TlTlAsSe 2 system

X-ray diffraction measurements of the liquid TlTlAsSe 2 system were carried out over the composition range from 0 to 80 mol%Tl. The electrical conductivity, magnetic susceptibility and thermoelectric power of this system were also measured over a wide temperature range. The first peak at 2.3 Å in the distribution function, G(r), observed in the low Tl concentration range below 40 mol%-Tl was assigned to the nearest neighbour AsSe interaction and the coordination number n AsSe=3 was obtained. This implies the AsSe chain structure in the solid state remains undestroyed on melting in this composition range. In the Tl rich region above 60 mol%Tl, the nearest neighbour AsSe peak becomes unclear and G(r) at 80 mol%Tl seems rather similar to that of pure Tl. The diffraction results and electronic properties observed suggest that the nearest neighbour TlTl interaction acts an important role in the Tl rich region.

Electrical and Magnetic Properties of Liquid Tl&amp;ndash;TlInTe&lt;SUB&gt;2&lt;/SUB&gt; and In&amp;ndash;TlInTe&lt;SUB&gt;2&lt;/SUB&gt; Systems

Electrical and Magnetic Properties of Liquid Tl&amp;ndash;TlInTe&lt;SUB&gt;2&lt;/SUB&gt; and In&amp;ndash;TlInTe&lt;SUB&gt;2&lt;/SUB&gt; Systems

Electronic Properties of Liquid TlGeTl2Se4 and TlSnTl2Se4 Systems

AbstractMeasurements of the electrical conductivity, magnetic susceptibility, and thermoelectric power for the liquid TlGeTl2Se4 and TlSnTl2Se4 systems are made in wide temperature and composition ranges. It is observed that the conductivity for both the systems has a minimum near the composition of 66.7 mol% Tl. However, the results of magnetic susceptibility reveal that the metalnonmetal transition of the present two systems occurs not at 66.7 mol% Tl but at 80 mol% Tl. The temperature dependence of thermoelectric power in both the systems is complex particularly in the composition range between 60 and 80 mol% Tl. The experimental results of the present work are compared with the previous data of liquid telluride systems and are discussed in the light of current transport theories employed in liquid semiconductors.

Magnetic susceptibility of liquid Bi, In, Sn and Tl

Precise measurements have been made on the magnetic susceptibility of liquid Bi, In, Sn and Tl using the Faraday method. Values are reported for each metal at the melting point and as a function of temperature above the melting point. The estimated error is less than one percent for Bi, In and Sn, and two percent for Tl. The experimental results give strong evidence that the magnetic properties of the liquid investigated are predictable using the free electron model. Some details of the susceptibility apparatus are described.