E. Bychkov

Chalcogenide glass chemical sensors: Research and analytical applications

The paper is devoted to research and development in the field of chalcogenide glass chemical sensors for determination of heavy metal ions in solution. The overview of the solid-state scientific approach and research design of the sensing materials is followed by the original results of the analytical application of the chalcogenide glass sensors for laboratory analysis, industrial control and environmental monitoring.

Analytical applications of chalcogenide glass chemical sensors in environmental monitoring and process control

The present paper deals with some aspects of the analytical application of chemical sensors based on chalcogenide glasses, including measurements in natural and waste waters of different factories both in laboratory and in situ modes. Determination of copper(II), iron(III), chromium(VI), lead, cadmium, and mercury starting at microgram concentration level has been carried out. The results of analysis with chalcogenide glass chemical sensors show a good agreement with those of atomic absorption spectroscopy and other common methods.

Ion transport regimes in chalcogenide and chalcohalide glasses: from the host to the cation-related network connectivity

Recent ionic conductivity and tracer diffusion measurements over a large range of the mobile ion content x, carried out for Ag + - and Cu + -conducting chalcogenide and chalcohalide glasses, show two distinctly different ion transport regimes above the percolation threshold at = 30 ppm M + : (i) a critical percolation regime at low x, and (ii) modifier-controlled ion transport at high x. Using a number of structural and spectroscopic techniques (high-resolution neutron diffraction, small-angle neutron scattering, high-energy X-ray diffraction, EXAFS, 129 I-Mossbauer spectroscopy), we will show that the two regimes have a clear structural basis. Transport properties in the critical percolation domain depend almost exclusively on the connectivity of the host matrix represented by the average coordination number : the nature of the mobile cations and chemical form of the dopant or of the host network do not play any important role. In contrast, the connectivity of the cation-related structural units MY z (Y = chalcogen or halide, z = 3 or 4), evidenced by the short M-M correlations (from 2.7 to 4.2 A) and reflected by the M-M coordination number, appears to be predominant in the modifier-controlled region. Highly connected edge- or corner-sharing (ES or CS) MY 2 units, which form at least 2D sheets or tunnels in the glass network, lead to the highest mobility of the M ions.

Thin-layer chemical sensors based on chemically deposited and modified chalcogenide glasses

Abstract A new type of chemically deposited and modified thin-layer sensors has been prepared and investigated. Amorphous As2S3 and AsSe thin films obtained by the spin-coating technique and doped with silver were used as membrane materials of these sensors. It was found that the temperature of preliminary annealing of the films is crucial for doping efficiency. As-prepared films annealed above 120 °C remain insulating after silver doping with subsequent annealing and/or light irradiation. XPS measurements indicated some kind of decomposition of arsenic chalcogenides in this case. Properly prepared and modified thin layers are mixed conductors with a final resistivity of about 105 ω cm for As2Se-based and ≈ 103 ω cm for AsSe-based films. Electrochemical measurements in AgNO3 solutions revealed a reasonable sensitivity of doped AsSe films to silver ions. The ionic response of doped As2S3 films was found to be significantly poorer. High electronic conductivity giving rise to competitive interfacial redox processes seems to be one reason for such behaviour. The redox response of the films was studied in solutions of potassium hexacyanoferrate(II)/(III) with total redox concentration from 0.1 to 0.001 M. The parameters of the redox response of selenide glass thin-layer sensors are close to those of platinum electrode at high total redox concentration and even better in dilute solutions.

Development and analytical evaluation of a multisensor system for water quality monitoring

Abstract Sensor arrays or multisensor systems form a dynamically developing group especially in the field of gas analyses, in recent years. However, only a few attempts to monitor liquid environments with the help of this method have been done. The present paper is devoted to some aspects of the development of multisensor systems for water quality monitoring on the basis of heavy metal-sensitive chalogenide glass materials.

Silver ion sensors based on AgAsSeTe glasses I. Ionic sensitivity and bulk membrane transport

Abstract AgAsSeTe glasses have been used as membranes of silver ion-selective electrodes. Sensors based on ion-conducting glasses with low tellurium content display high Ag+ ion sensitivity, potential stability and reproducibility. They are superior to crystalline silver-ion sensors in selectivity in the presence of interfering ions, such as mercury(II), iron(III) and copper(II) ions. Semiconducting Te-rich glasses show some features in silver ion response (super-Nernstian slope in diluted solutions, less stable potentials, etc.) that are explained by competitive redox processes at the glass/solution interface. Deterioration of the response is related both to increases in electronic conductivity and to decreases in ionic conductivity. A lack of chemical stability of the surface of Te-rich glasses can also play a certain role.

Chalcogenide glass chemical sensors: Relationship between ionic response, surface ion exchange and bulk membrane transport

Abstract Different factors affecting chalcogenide glass chemical sensor response are discussed. It is shown that definite relationships between composition, glass structure, chemical durability, bulk and surface ionic processes, and sensor performance exist. All these factors are connected to each other in a complicated way; therefore, further development of new sensors with improved analytical characteristics needs a detailed study of the chemical and physical properties of the glasses.

Mechanism studies on lead ion-selective chalcogenide glass sensors

Abstract The lead ion-sensing mechanism of PbSAs2S3, AgAsS2 and PbSAg2SAs2S3 chalcogenide glass sensors has been studied. The following principal methods have been chosen: (i) a study of the sensitivity of Ag-free PbSAs2S3 glasses to lead ions in solution; (ii) an investigation of induced exchange-site formation using XPS, AES and SIMS; (iii) 212Pb tracer measurements to obtain information about lead ion exchange. It has been shown that Ag-free PbSAs2S3 glasses are sensitive to Pb2+ ions in solution; their standard potentials are close to those of Ag-containing vitreous alloys. The formation of induced exchange sites governing the lead-ion sensitivity of Pb-free AgAsS2 glass sensors has been confirmed by surface spectroscopies. Evidence for direct Pb2+ ion exchange at the membrane/solution interface for both PbSAg2SAs2S3 and AgAsS2 glasses has been obtained by tracers. All these experiments indicate that the ion response of lead ion-selective chalcogenide glass sensors can be completely described within the framework of the modified surface-layer model.

Ni-implanted vitreous electrolyte AgAsS2: ECR, ionic and electronic conductivity

Abstract Transport properties of AgAsS 2 glassy solid electrolyte implanted with 60 keV nickel ions at dose of 10 17 Ni/cm 2 were studied. The increase of ionic conductivity by 2.5 orders of magnitude and simultaneous activation energy decrease from 0.34 to 0.18 eV have been observed. The ionic conductivity enhancement is related to two-phase morphology of implanted layer which leads to formation of “infinite” perculation cluster with low-energy barriers for Ag + ion motion. AgAsS 2 glass reveals p -type electronic conductivity, σ p . Nickel ion implantation increases σ p by six orders of magnitude. The enhancement of hole transport has been explained involving small-polaron hopping between Ni 2+ and Ni 3+ ions. Temperature dependence of Ni 3+ ESR line intensity is in agreement with polaron mechanism of σ p in Ni-containing chalcogenide glasses. ESR results showed also that charge state and coordination of impurity nickel ions in Ni-implanted and thermally-doped AgAsS 2 glasses are identical.

Unraveling the atomic structure of Ge-rich sulfide glasses

In contrast to the well-established structure of glassy GeS2, consisting of corner- and edge-sharing GeS(4/2) tetrahedra, the structural features of Ge-rich sulfide alloys remain essentially unknown. Two contrasting points of view: (1) a tetrahedral model, and (2) a distorted NaCl approach were neither confirmed nor excluded mostly because of missing advanced structural studies. Using high-energy X-ray scattering and neutron diffraction, we show the complexity of the short and intermediate range order in Ge(x)S(1-x) glasses, ⅓ ≤ x ≤ 0.47, formed by corner- and edge-sharing tetrahedra with two-fold coordinated sulfur species and a variable number of Ge-Ge bonds, and Ge-S units with three-fold coordinated sulfur at x ≥ 0.36.