The Electrical Conductivity of Liquid Tin: (Ii) Sulphide

Abstract

'I'he electrical conductivity "v" of tin (11) sulphidc in the liquid state has bee11 measured using a capillary type cell. Both a-c. and d-c. methods \lrere ~~s e d .The conductivity of SnS increases reg~~larly \\rith t e~n p e r a t~~r e , from approximately 24 ohm-I cm-I a t 895' C to 31.2 ohm-' c~n-I a t 930' C. The similarity of results obtained with both a-c. and d-c. methods, the positi\;e te~nperature coefficient of conductivity, the high value of the cor~ductivity and the absence of electrolysis effects when passing heavy currents i n the melt lead to the conclusion that SnS remains a semiconductor in the liquid state. The value of the energy gap has been calculated t o be 1.9 ev for the liquid as compared to the value 1.2 e.v for the solid. Conductivity nleasurements have been lirnited t o the temperature of appros~mately 935' C I~ecause of the decomposition of SnS a t higher tenlperatures. INTRODUCTIONStudy of the electrical properties of liquid inorganic salts and oxides has shown t h a t these chemical compounds are often ionic in the liquid state a s evidenced by the high value of the conductivities, the positive tenlperature coefficients of conductivity, and the high current efficiencies ( 1 , 2 , 3 ) . T h e electrical conductivity of a few metallic sulphides in the liquid state has been investigated: NiS (9), Bi2S3 (9), and FeS (4, 5 , 7 ) have been reported to behave a s typical metallic conductors while Cu2S ( 4 , 5 , 6) and TlsS (10) have been shown t o be semiconductors. Liquid antimony (111) sulphide SbSSP has a lnixecl conductivity, ionic and electronic (8).Tin (11) sulphide SnS is Iinown to be a semiconductor in the solid state (11) and has been reported to possess mixed conductivity in the liquid state (9). In order to deterlnine whether this compound retains its semiconductivity in the liquid state it was planned to stucl!~ its electrical conductivity more tl~oroughly than was clone by previous worlcers. EXPERIMENTAL Prcpurutiolt of SnST h e tin (11) sulphide used ill this study was prepared b y direct synthesis from the elements: "Reagent" grade tin and recrystallized sulphur were usecl. T h e tin sulphide so obtained contains free sulphur and some SnS2. Consequently, the crude sulphide mas heated under vacuum a t 450° C t o eliminate the free sulphur and melted under a nitrogen atmosphere a t 1000° C, this temperature being maintained between 1 and 2 hours in order to decompose the tin (IV) sulphide to tin (11) sulphide and sulphur. T h e furnace temperature was then brought down to 890' C and a partial vacuum was maintained over the melt t o eliminate the last traces of sulphur. T h e tin (11) sulphide was then distilled a t the same temperature under high vacuum using a graphite condenser. T h e tin (11) sulphide thus prepared has a metallic appearance and is completely soluble in concentrated I-ICI. Two batches of sulphide were prepared and showed identical X-ray powder patterns (114.8-mm camera, Cu radiation, Ni filter): these patterns were strictly identical with the l a ...

Molten Semiconductors for High Temperature Thermoelectricity

“…Figure 6b shows an increase of the maximum melt power calculated with the electrical conductivity of molten SnS reported previously. 19 The Figure (Figure 6b, black squares) after excluding device-level contributions (e.g. power and resistance from graphite, nickel and copper) instead of the maximum power generated at the device level (Figure 5b).…”

“…Figure 6b shows an increase of the maximum melt power calculated with the electrical conductivity of molten SnS reported previously. 19 The Figure of Merit in Figure 6b is evaluated from Equation 2 and Equation 7, using the Seebeck coefficient measured in the present work, the literature electrical conductivity, and the experimental efficiency. It should be clarified that this Figure of Merit represents the molten material itself present inside a device and is obtained based on the maximum power generated by the melt alone (Figure 6b, black squares) after excluding device-level contributions (e.g.…”

“…Indeed, the most common synthesis route to obtain molten semiconductors is by mixing the pure components at the desired ratio prior to a melting process. [19][20][21][22][23] Molten semiconductors attracted great research interest in the late 1950s and 1960s. Two fundamental ideas have shaped the knowledge of molten semiconductors.…”

“…As shown in Table I, other molten sulfide systems that also exhibit semiconducting properties such as Ni-S, Co-S, Sn-S, Ag-S, Pb-S [19][20][21]29,30 are of interest from both a cost and performance perspective. Unfortunately, a dearth of experimental or modeling physical and chemical property data currently limits our ability to further support the development of molten sulfides as potential thermoelectric materials.…”

Experimental study of molten tin sulfide thermal conduction

“…The electrode and container is graphite, a material that is chemically and mechanically stable in presence of liquid sulfides. The apparent thermal conductivity of the SnS melt can be estimated from the electrical conductivity reported by Boutin and Bourgon 70 where TH is the hot-side temperature, TC is the cold-side temperature, ̅ is the figure of merit at the average temperature ̅ , is the Seebeck coefficient, is the electrical conductivity.…”