Graded ferroelectric capacitors with robust temperature characteristics

Ferroelectric thin films offer the possibility of engineering the dielectric response for tunable components in frequency-agile rf and microwave devices. However, this approach often leads to an undesired temperature sensitivity. Compositionally graded ferroelectric films have been explored as a means of redressing this sensitivity, but experimental observations vary depending on geometry and other details. In this paper, we present a continuum model to calculate the capacitive response of graded ferroelectric films with realistic electrode geometries by accurately accounting for the polarization distribution and long-range electrostatic interactions. We show that graded c-axis poled BaxSr_(1−xT)iO_3 BST parallel plate capacitors are ineffective while graded a-axis poled BST coplanar capacitors with interdigitated electrodes are extremely effective in obtaining high and temperature-stable dielectric properties

Two-Proton Radioactivity with 2p halo in light mass nuclei A==18−-34

Two-proton radioactivity with 2p halo is reported theoretically in light mass nuclei A $=$ 18-34. We predict $^{19}$Mg, $^{22}$Si, $^{26}$S, $^{30}$Ar and $^{34}$Ca as promising candidates of ground state 2p-radioactivity with S$_{2p}$ $$ 0. Observation of extended tail of spatial charge density distribution, larger charge radius and study of proton single particle states, Fermi energy and the wave functions indicate 2p halo like structure which supports direct 2p emission. The Coulomb and centrifugal barriers in experimentally identified 2p unbound $^{22}$Si show a quasi-bound state that ensures enough life time for such experimental probes. Our predictions are in good accord with experimental and other theoretical data available so far.Comment: 5 Pages, 5 figure

Study of bone turnover markers, procollagen type 1 N-terminal propeptide and osteocalcin in healthy and type 2 diabetes mellitus postmenopausal women

Background: Individuals with diabetes mellitus are at increased risk of metabolic bone disease due to decrease in bone strength and quality. Several bone turnover markers like serum procollagen type I N propeptide (P1NP) and serum osteocalcin are powerful tools for studying osteoporosis and fracture risk across population to provide diagnostic and prognostic information of bone health. The aim of this study was to recognize possible correlation of levels of serum P1NP and osteocalcin in type-2 diabetic (T2DM) postmenopausal women as compared to healthy postmenopausal women.Methods: The study included 100 proven cases of type-2 diabetic postmenopausal women with age matched healthy postmenopausal women as controls. P1NP, osteocalcin, and other relevant parameters were measured. Differences between diabetics and controls were analyzed.Results: The body mass index was higher in diabetic group as compared to controls. The HbA1c% was (6.94±1.43) in diabetic group and (5.57±1.21) in non-diabetics. Low serum level of 25 (OH) D was observed both in diabetic and non-diabetic groups but significantly lower in T2DM. Procollagen type 1 N propeptide was lower in diabetic group (37.59±17.20 ng/mL) as compared to non-diabetic (52.14±24.82 ng/mL). Osteocalcin was lower (15.64±8.06 ng/ml) as compared to non-diabetic group (21.85±9.12 ng/ml). Lower osteocalcin and P1NP levels found in this study suggests slower bone metabolism with reduced bone formation in postmenopausal diabetics.Conclusions: Serum procollagen type 1 N propeptide and osteocalcin in postmenopausal diabetic women were lower as compared to non-diabetic group

Electromechanical behavior of 90-degree domain motion in barium titanate single crystals

It is well known that many common ferroelectric materials are also ferroelastic, thus the nonlinear behavior of these materials, as governed by domain motion, is highly affected by stress, as well as electric field. The combined influence of stress and electric field on domain motion and the electrostrictive response of ferroelectric single crystals is investigated. Experiments are performed on (001) and (100) oriented single crystals of barium titanate under combined electro-mechanical loading. The crystal is exposed to a constant compressive stress and an oscillating electric field along the [001] direction. Global deformation and polarization are measured as a function of electric field at different values of compressive stress. The use of semi-transparent electrodes and transmitted illumination allow in situ, real-time microscopic observations of domain motion using a long working-distance, polarizing microscope. The combined electro-mechanical loading results in a cycle of stress and electric field induced 90-degree domain switching. The magnitude of the global deformation increases with stress, with maximum steady state actuation strain of 0.57%