H. Jain

Vector Piezoresponse Force Microscopy

A novel approach for nanoscale imaging and characterization of the orientation dependence of electromechanical properties-vector piezoresponse force microscopy (Vector PFM)-is described. The relationship between local electromechanical response, polarization, piezoelectric constants, and crystallographic orientation is analyzed in detail. The image formation mechanism in vector PFM is discussed. Conditions for complete three-dimensional (3D) reconstruction of the electromechanical response vector and evaluation of the piezoelectric constants from PFM data are set forth. The developed approach can be applied to crystallographic orientation imaging in piezoelectric materials with a spatial resolution below 10 nm. Several approaches for data representation in 2D-PFM and 3D-PFM are presented. The potential of vector PFM for molecular orientation imaging in macroscopically disordered piezoelectric polymers and biological systems is discussed.

Tracer diffusion and electrical conductivity in sodium-cesium silicate glasses☆

Abstract The tracer diffusion coefficients of 22Na and 137Cs, and the electrical conductivity have been measured in the (Na, Cs)2O:3SiO2 glasses as a function of temperature and Cs/Na ratio. Complex impedance analysis was used for the conductivity measurements. The Haven ratio at 396.5°C increases from 0.3–0.4 in single-alkali glasses to 0.8 for the mixed-alkali compositions. The results are explained in terms of a single-jump mechanism; interactions between alkali ions and non-bridging oxygen ions, and between different alkali ions, produce the observed correlation effects.

Transparent Ferroelectric Glass-Ceramics

In recent years, there has been a resurgence of interest in transparent ferroelectric glass-ceramics (TFGCs), which are a special class of glass-ceramic composites that combine the low cost of fabrication and forming of transparent glass with the superior nonlinear optical and electro-optical properties of ferroelectric crystals. In this paper, we present a review of the current status, focusing on the challenges of fabrication and opportunities for selectively creating nonlinear optical structures, which will be useful in realizing integrated optical devices. A successful fabrication of TFGC requires the nucleation and growth of crystallites that are too small to scatter light, yet large enough to have ferroelectric response. Early experiments on silica based glasses containing common ferroelectric oxides indicated that although the preparation of TFGC is feasible, such a balance of crystallite size is difficult to achieve. However, later studies have demonstrated successful fabrication of TFGCs with compositions based on high refractive index glass matrix (e.g. tellurites containing ferroelectric LiNbO3), or the ferroelectric oxides that form glass easily and then crystallize congruently (e.g. LaBGeO5). Surface crystallization dominates the devitrification of these compositions. Strong second harmonic generation of light has been observed in a number of glass-ceramic systems, which makes them attractive for applications but so far the ferroelectric behavior has been demonstrated for very few systems.

Analysis of ac conductivity of glasses by a power law relationship

The frequency dependence of electrical conductivity of many germanate and borate glasses has been analyzed in terms of an empirical power law at different temperatures. The power law has often been used in determining the concentration of mobile carriers in various materials, but our analysis does not agree with some of the assumptions and, hence, limits the physical interpretation of the law.

Characterization of new erbium-doped tellurite glasses and fibers

Tellurite glasses are promising candidates for optical fiber laser and amplifier applications because of their excellent optical and chemical properties. The emission spectrum from erbium in tellurite glasses is almost twice as broad as the corresponding spectrum in silica. In this presentation, we report the results of a two-prong investigation of new tellurite glasses: a Raman study that provides detail information on the microscopic structure of these glasses, and a study of the erbium emission in fibers fabricated from these glasses. Specifically, we report on the emission from fibers of different lengths and for different pumping schemes.

Vibrational study of the role of trivalent ions in sodium trisilicate glass

Abstract The structure of glasses in the system Na 2 O · x R 2 O 3 · (3 − 2 x )SiO 2 (RAl, B) has been studied by employing Raman and infrared reflectance spectroscopies. These particular glass compositions were chosen for elucidating the role of aluminum and boron substitution on glass structure and properties while keeping the Na/(Si + R) ratio fixed. In the presence of aluminum, the equilibrium 2Q 3 ⇔ Q 4 + Q 2 shifts to the left. The role of boron was found to be the opposite, since it induces the destruction of the Q 3 species and the creation of the highly charged Q 2 and Q 1 species, as well as the fully polymerized Q 4 silicate units. The combined far-infrared and XPS results on the same glasses suggest that the average charge density of sites populated by sodium ions is smaller in aluminosilicate than in borosilicate glasses.

‘Window’ effect in the analysis of frequency dependence of ionic conductivity

Abstract Usually the frequency dependence of ionic conductivity of solids in analyzed in the form of a power law or as the deviation of imaginary part of electric modulus from ideal Debye peak. The power law formalism is shown to be sensitive to the choice of frequency window employs in the analysis. The results demonstrate the inadequacies of either formalism and a method is suggested of combining the two formalisms for parameterizing non-ideal electric response in the vicinity of the electrical conductivity relaxation time.

Role of S/Se ratio in chemical bonding of As-S-Se glasses investigated by raman, x-ray photoelectron, and extended x-ray absorption fine structure spectroscopies

Chalcogenide glasses have attracted considerable attention and found various applications due to their infrared transparency and other optical properties. The As–S–Se chalcogenide glass, with its large glass-formation domain and favorable nonlinear property, is a promising candidate system for tailoring important optical properties through modification of glass composition. In this context, a systematic study on ternary As–S–Se glass, chalcogen-rich versus well-studied stochiometric compositions, has been carried out using three different techniques: Raman spectroscopy, x-ray photoelectron spectroscopy, and extended x-ray absorption fine structure spectroscopy. These complementary techniques lead to a consistent understanding of the role of S∕Se ratio in chalcogen-rich As–S–Se glasses, as compared to stochiometric composition, and to provide insight into the structural units (such as the mixed pyramidal units) and evidence for the existence of homopolar bonds (such as Se–Se, S–S, and Se–S), which are the ...

Low temperature A.C. conductivity of oxide glasses

The electrical conductivity (σ) of various alkali silicate, borate and germanate glasses has been measured from 3 K to 300 K in the frequency range 10–100 kHz. Mostly the frequency (ω) and temperature (T) dependence of conductivity below 150 K can be described as σ ~ Tαωβ where 0 < α < 0.25 and 1.0 < β < 1.15. An abnormal decrease of conductivity with increasing temperature is observed at about 100–150 K in glasses with low alkali oxide concentration (< 1 mol%). A theoretical model based on thermally activated excitations of asymmetric double well potential (ADWP) configurations has been used to explain the low temperature conductivity data. From the alkali concentration and size dependence of the parameters in ADWP model, a physical description of the species responsible for low temperature a.c. conductivity is obtained.

Electrical conductivity of synthetic and natural quartz crystals

Electrical conductivity of α quartz is ionic, the current being carried by alkali ions (M+) moving in channels parallel to the c axis. A study was made of conductivity σ of one natural and three synthetic crystals in order to better understand these ionic defects. ac measurements were made over a wide range of frequencies, and complex‐impedance analysis was used to separate out the bulk conductivity from electrode effects. The activation energy E for the synthetic crystals was always close to 1.36 eV and the pre‐exponential A was in the range of 106 K/Ω cm. A decrease in σ resulted from electrodiffusion (sweeping) in hydrogen. For the as‐received natural crystal, the value of E was 0.82 eV, but this E value increased appreciably after hydrogen sweeping or after irradiation plus high‐temperature anneal. The principal observations could not be interpreted in terms of the conventional theory in which the Al3+‐M+ pair and its dissociation products are the only defects involved. A modified theory, in which add...