Superionic Conductor RbAg4I5 Research Articles

Enhanced self-powered ion-modulated photodetector based on an asymmetric composite structure of superionic conductor RbAg4I5 and graphene.

Traditional strategies for self-powered devices face limitations in performance improvement due to the trade-off relationship between different parameters. Here, a new kind of ion-modulation self-powered photodetector is first proposed and fabricated by depositing superionic conductor RbAg4I5 on one side of monolayer graphene. The graphene homojunction is successfully formed at the boundary of the asymmetric structure due to the formation of bound states of ions and electrons at the contact interface. This kind of homojunction avoids the trade off between response parameters of traditional self-powered devices because the dissociation of bound states under light irradiation dominates the generation of a photocurrent. The experimental results indicate that the prepared photodetector can achieve great photo response with responsivity of 20 mA/W and a response speed of 700 µs for ultraviolet and visible light when no bias is applied, which is better than most existing graphene-based self-powered devices in single or overall parameters. Further, a semi-quantitative model is systematically established according to the internal mechanism and realizes a good consistency with experimental results. The work provides a new idea and offers the foundation to develop excellent self-powered devices based on superionic materials with good properties in controllability and modulation.

Optical Modulation of Charge Transport in Layered Graphene System by Superionic Conductor RbAg4I5

AbstractHerein, the photoelectric performances of n‐layer graphene and RbAg4I5 composite nanostructures are schematically studied from experimental and theoretical perspectives. Relevant layer‐dependence studies reveal the suitability of the superionic conductor RbAg4I5 to modulate electron transport in graphene. The critical factors of induced charge carriers and their screening effects significantly impact the optoelectronic properties of the composite nanostructure. Further, the presence of an optimal graphene thickness is predicted for designing an ion‐modulated graphene photodetector. This work paves the way for further development of high‐performance photodetectors based on multilayer graphene and superionic conductors.

Self-assembled gold micro/nanostructure arrays based on superionic conductor RbAg4I5 films

Herein, we propose a new strategy to fabricate gold (Au) micro/nanostructure arrays by photocatalytic solid-state electrochemical reaction between superionic conductor RbAg4I5 and Au films. The Au and RbAg4I5 films were successively deposited on a clean quartz substrate by vacuum thermal deposition method. A copper microgrid possessing periodic holes 100 μm in diameter was put above the RbAg4I5 film as a mask plate, whereupon irradiation from a 405 nm wavelength laser was used to diffuse gold ions (Au+ ions) into vacant silver sites of RbAg4I5 and transfer Au+ through ion passageways in the RbAg4I5 film. When the laser was turned off, the Au+ ions were easily reduced due to low activity compared to the silver (Ag+) ions. After multiple on/off cycles of the 405 nm laser, the irradiated area of uniform Au film exhibited a periodic structural unit array whose period was the same as that of the mask plate hole array. Atomic force microscope and scanning electron microscope images revealed that a self-assembled needle-like nanostructure array grew perpendicular to the substrate surface inside each circle’s structural unit. The height of the grown nanostructure array increased with laser power density. Raman enhancement of the gold nanostructure array as substrate was detected using Rhodamine 6G (R6G) ethanol solutions as probe molecules. The enhancement effect increased with the height of the grown nanostructure array, and could increase by two orders of magnitude greater than that of unirradiated Au film. This strategy offers a new method for the micro/nanostructure processing of gold and provides microscale-array-mediated surface-enhancement Raman-scattering (SERS) substrates comprising Au nanostructures for application in high-sensitivity spectrum analysis.

Enhanced photoelectric performance of composite nanostructures combining monolayer graphene and a RbAg4I5 film

In the fields of electronics and optoelectronics, graphene has attracted much attention as a potential alternative material. Using the vapor deposition method, a monolayer graphene-based nanostructure modified by the superionic conductor RbAg4I5 is developed. At a small bias of 0.2 V, it exhibits excellent photoelectric characteristics at selected wavelengths 532 nm, 785 nm, and 808 nm in the spectral region from visible green to near infrared. Taking 532 nm as an example, the responsivity is 1.2 mA W−1 (an improvement of greater than 400 times) and the response time is 15 ms (a decrease of less than one order of magnitude), significantly superior to those of pristine monolayer graphene. Experimental and theoretical studies show that the dissociation and recombination of ion-electron bound states lead to nonlinear photon current with universal behavior in the composite nanostructure. These results pave the way for exploiting high-performance photodetectors based on monolayer graphene and RbAg4I5 film composite nanostructures.

Ion-modulated nonlinear electronic transport in carbon nanotube bundle/RbAg4I5 thin film composite nanostructures

We have explored the ion-modulated electronic transport properties of mixed ionic-electronic conductor (MIEC) composite nanostructures made of superionic conductor RbAg4I5 films and carbon nanotube (CNT) bundle spiderwebs. Our experimental and theoretical studies indicate that the formation of ion-electron bound states (IEBSs) leads to strong ion-electron interference effect and interesting electronic transport of CNT, such as nonlinear current-voltage (I–V) characteristics and novel temperature dependence of the current. With increasing temperature, the hybrid nanostructures show rich phases with different dependence of current on temperature, which is related to the structural phase transition of RbAg4I5 and the transition of dissociation of IEBSs. The ion-modulation of the electric conductivity in such MIEC composite nanostructures with great tunability has been used to design new ionic-electronic composite nano-devices with function like field effect transistor.

Experimental thermodynamic study of the equilibrium phase AgBi3S5 by an improved EMF method

A thermodynamic study of the equilibrium phase assemblages AgBi3S5–Bi2S3–S/Bi was made by an EMF-technique. The ternary phase was synthesized from the pure Ag2S and Bi2S3 in an evacuated silica ampoule, and ground into powder before mixing with appropriate compositions of Bi2S3 and S or Bi. The phase mixtures were pressed into different pellets, in a series of experiments. Together with pieces of pure Ag-foil and the electrolytic pellets of superionic conductor RbAg4I5 or AgI, the pellets were assembled to form the galvanic cells Pt(−)|Ag|RbAg4I5|AgBi3S5+Bi2S3+S+(C)|Pt(+) and Pt(−)|Ag|AgI|AgBi3S5+Bi2S3+Bi|C|Pt(+). The EMF-measurements were made in a temperature range 299.15–594.15K. In this paper, the thermodynamic functions for the formation of pavonite (AgBi3S5) at sulfur and bismuth saturation have been determined. The obtained results are in agreement with some of the available literature values. Furthermore, new experimental thermodynamic data of bismuth-saturated pavonite (AgBi3+xS5; 0<x<0.14), in the temperature range 299.15–594.15K, were determined.

Thermodynamic stability of Ag2Se from 350 to 500 K by a solid state galvanic cell

The numerical values on the standard thermodynamic functions of Ag2Se (naumannite) were determined by the electromotive force (EMF) method in a solid-state galvanic cell with superionic conductor RbAg4I5 as the solid electrolyte. Ag2Se was synthesized from pure elements in evacuated quartz glass ampoules and examined to be homogenous by SEM and EDS. According to the experimental data on the EMF versus temperature, the analytical equations were obtained for the polymorphic forms of Ag2Se. The temperature-dependent relationships of the Gibbs energy of formation of Ag2Se in its polymorphic forms and the standard thermodynamic functions of compounds within the temperature range of 350–500K were also evaluated. The temperature of phase transformation from α-Ag2Se to β-Ag2Se is determined experimentally to be 407.7K and the enthalpy of phase transformation is 6.06kJmol−1.

Electronic absorption spectrum of solid solutions of the system RbI–AgI–CsI

The absorption spectrum in the region of the fundamental electronic bands are investigated in solid solutions of compounds in the system RbI–AgI–CsI, specifically, in the solid solutions Rb2−2xCs2xAgI3 in the concentration interval 0⩽x⩽1, RbxCs1−xAg2I3 for 0⩽x⩽0.9, and Rb1−xCsxAg4I5 for 0⩽x⩽0.2. In all cases a short-wavelength shift of the exciton bands and growth of the band gap Eg with increasing Cs+ concentration are observed. In RbxCs1−xAg2I3 an anomalous concentration dependence of the half-width of the exciton bands is observed, due to a tendency toward the formation of an ordered solid solution for x=0.5. A Cs+ impurity lowers the stability of the superionic conductor RbAg4I5 and promotes its decomposition into the compounds AgI and Rb2AgI3, but for x&amp;lt;0.2 it does not affect the temperatures of the phase transitions or the activation energy for Frenkel defects in the superionic state.

Preparation and Structural Characterization of SuperionicConductor RbAg4I5 Crystalline Grain Film

Superionic conductor RbAg4I5 crystalline grain films wereprepared by vacuum thermal evaporation on NaCl crystalline substrates.The surface morphology, microstructure and the electronic energy statesof the films were examined by atomic force microscopy, transmission-electron microscopy, x-ray diffraction and x-ray photoelectronspectroscopy. The results show that the obtained RbAg4I5layer has an epitaxial film of perfect crystalline structure, and theunit cell of crystalline grain RbAg4I5 films belongs tocubic crystal system. The principal x-ray diffraction peaks atd = 3.7447 and 1.8733 Å are related to the structure of ternarycompound RbAg4I5 films.

Mössbauer Diffraction in the Superionic Conductor RbAg4I5

AbstractThe problem of Mössbauer diffraction on crystals with intensive diffusion is analysed for the case of the superionic conductor RbAg4I5. An expression for the Mössbauer spectra of the diffracted beam is given for different diffusional model. The experimental temperature dependence of the coherent scattering of Mössbauer radiation in this sample is interpreted on the basis of developed theoretical assumptions.

Thermodynamic approach to quasielastic light scattering from crystals

Abstract Nonequilibrium thermodynamics (NETD) is utilized in theanalysis of the spectrum of light scattered quasielastically by crystals. This thermodynamic approach involves: (i) determination fo the equations satisfied by the crystal's thermodynamic variables, taking irreversible processes into account; (ii) solution of such equations for the chosen scattering vector and the relevant crystalline symmetry, and (iii) determination of the spectrum by means of the Onsager hypothesis relating the soluitons obtained and the correlation functions of the same variables. Several applications of the methodoloy are discussed. The ferroelectric KH2PO4 is considered both as a typical crystal exhibiting the standard spectrum consisting of a Rayleigh line and two Brillouin lines and also as a piezoelectric crystal, in which case an additional line a polarization relaxation line–is present in the spectrum. Another relaxation process is also considered: that associated with hopping diffusion in the superionic conductor RbAg4I5. The critical region is also discussed, in the context of the Ornstein-Zernike approximation. The applications illustrate the power and basic simplicity of the NETD approach: in many situations of interest, the parameters that come into play possess transplrent physical meaning and the spectra can be completely determined by trivial algebraic manipulations. This is to be contrasted with the standard phenomenological coupled-mode approch to quasielastic light scattering, invovling more complex manipulations and parameters whose physical meaning is often unclear and which are usually only very indirectly related to quantities measured using other experimental techniques.

Crystal structure of the superionic conductor RbAg4I5 in the temperature range from ?45 to +135�

Crystal structure of the superionic conductor RbAg4I5 in the temperature range from ?45 to +135�

Electrical conductivity and optical absorption studies in superionic RbAg4I5 thin films

Electrical conductivity in thin films of the superionic conductor RbAg4I5 was found to be in very good agreement with the best bulk value (0.27 Ω−1 cm−1). From the conductivity data, the activation energy for Ag+-ion conduction, and the free-ion-like parameters such as the mean free path and lifetime in the excited state have been deduced. The phase transition at 210 °K has also been observed, and the activation energy for conduction before and after the phase transition has been evaluated. Optical absorption studies in these films reveal a well-defined exciton state at 3750 Å at 300 °K. Also, a weak band is observed at 3350 Å on the higher-energy side of the exciton band which appears to be evidence for the existence of large-radius excitons. A broad band observed at 4850 Å has been attributed to the existence of silver colloids in the films. A forbidden internal transition in the Ag+ ion has been observed at 4250 Å.

Evidence for a first-order phase transition at 209 K in the superionic conductor RbAg4I5

By nuclear quadrupole resonance we have found evidence that the structural phase transition at 209 K in RbAg 4 I 5 is of first rather than of second order. In addition, the point group symmetry of the Rb site in the α-phase is lower than 3. Finally, a preliminary value of 25 MHz for the inverse correlation time of the Ag ion diffusion is obtained at 150 K.

Stability and optical absorption of the super-ionic conductor RbAg4I5

An optical method for the study of decomposition of the super-ionic conductor RbAg4I5 into Rb2 AgI3 and AgI is described. The rate of decomposition is determined by observing the growth of the exciton peak of AgI. The optical absorption in single-crystal RbAg4I5 is also reported at temperatures of 295, 253 and 77K.

Comment on second order phase transition in the super ionic conductor RbAg4I5

Comment on second order phase transition in the super ionic conductor RbAg4I5