Effect of Lanthanum Substitution on the Structural, dielectric, Ferroelectric and Piezoelectric Properties of Mechanically Activated PZt Electroceramics

Different compositions of (Pb1-xLax) (Zr0.60Ti0.40)O3 (abbreviated as PLZT x/60/40; x=0, 0.07, 0.08 and 0.10) ceramics were prepared by a combinatorial approach by high energy mechano-chemical ball milling and cold isostatic pressing (CIP). X-ray diffraction patterns and transmission as well as scanning electron microscope were used for the micro-structural and morphological studies. The average particle size of PLZT milled powders was measured from the TEM images and was found to be in the nm range.XRD patterns of the sintered PLZT x/60/40 ceramics confirm the perovskite phase formation after heat treatment. SEM of sintered PLZT x/60/40 ceramics show a close packed dense structure. PLZT 8/60/40 ceramics show the fine grains (~1.3 µm) with density ~97 per cent. Dielectric constant and loss were measured as a function of temperature. PLZT 8/60/40 ceramics shows the highest value of room temperature dielectric constant ~2480 at 1 kHz. Ferroelectric studies were done with the help of polarisation (P-E) and strain (S-E) vs. electric field measurements. PLZT 8/60/40 ceramics shows the maximum value of remnant polarisation (~36 µC/cm2) and strain (~0.27 per cent), respectively. PLZT x/60/40 ceramic samples were poled at optimized poling conditions. The measured values of piezoelectric charge coefficient (d33) and electromechanical coupling factor (kp) of PLZT 8/60/40 ceramics were found to be, ~690 pC/N and ~71 per cent, respectively

Global, regional, and national age-sex-specific mortality and life expectancy, 1950–2017: a systematic analysis for the Global Burden of Disease Study 2017

BACKGROUND: Assessments of age-specific mortality and life expectancy have been done by the UN Population Division, Department of Economics and Social Affairs (UNPOP), the United States Census Bureau, WHO, and as part of previous iterations of the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD). Previous iterations of the GBD used population estimates from UNPOP, which were not derived in a way that was internally consistent with the estimates of the numbers of deaths in the GBD. The present iteration of the GBD, GBD 2017, improves on previous assessments and provides timely estimates of the mortality experience of populations globally. METHODS: The GBD uses all available data to produce estimates of mortality rates between 1950 and 2017 for 23 age groups, both sexes, and 918 locations, including 195 countries and territories and subnational locations for 16 countries. Data used include vital registration systems, sample registration systems, household surveys (complete birth histories, summary birth histories, sibling histories), censuses (summary birth histories, household deaths), and Demographic Surveillance Sites. In total, this analysis used 8259 data sources. Estimates of the probability of death between birth and the age of 5 years and between ages 15 and 60 years are generated and then input into a model life table system to produce complete life tables for all locations and years. Fatal discontinuities and mortality due to HIV/AIDS are analysed separately and then incorporated into the estimation. We analyse the relationship between age-specific mortality and development status using the Socio-demographic Index, a composite measure based on fertility under the age of 25 years, education, and income. There are four main methodological improvements in GBD 2017 compared with GBD 2016: 622 additional data sources have been incorporated; new estimates of population, generated by the GBD study, are used; statistical methods used in different components of the analysis have been further standardised and improved; and the analysis has been extended backwards in time by two decades to start in 1950. FINDINGS: Globally, 18·7% (95% uncertainty interval 18·4–19·0) of deaths were registered in 1950 and that proportion has been steadily increasing since, with 58·8% (58·2–59·3) of all deaths being registered in 2015. At the global level, between 1950 and 2017, life expectancy increased from 48·1 years (46·5–49·6) to 70·5 years (70·1–70·8) for men and from 52·9 years (51·7–54·0) to 75·6 years (75·3–75·9) for women. Despite this overall progress, there remains substantial variation in life expectancy at birth in 2017, which ranges from 49·1 years (46·5–51·7) for men in the Central African Republic to 87·6 years (86·9–88·1) among women in Singapore. The greatest progress across age groups was for children younger than 5 years; under-5 mortality dropped from 216·0 deaths (196·3–238·1) per 1000 livebirths in 1950 to 38·9 deaths (35·6–42·83) per 1000 livebirths in 2017, with huge reductions across countries. Nevertheless, there were still 5·4 million (5·2–5·6) deaths among children younger than 5 years in the world in 2017. Progress has been less pronounced and more variable for adults, especially for adult males, who had stagnant or increasing mortality rates in several countries. The gap between male and female life expectancy between 1950 and 2017, while relatively stable at the global level, shows distinctive patterns across super-regions and has consistently been the largest in central Europe, eastern Europe, and central Asia, and smallest in south Asia. Performance was also variable across countries and time in observed mortality rates compared with those expected on the basis of development. INTERPRETATION: This analysis of age-sex-specific mortality shows that there are remarkably complex patterns in population mortality across countries. The findings of this study highlight global successes, such as the large decline in under-5 mortality, which reflects significant local, national, and global commitment and investment over several decades. However, they also bring attention to mortality patterns that are a cause for concern, particularly among adult men and, to a lesser extent, women, whose mortality rates have stagnated in many countries over the time period of this study, and in some cases are increasing

Microwave characterisation of dielectric materials - an overview

Dielectric materials are the backbone of all high frequency communicatiol1 devices and circuits. The size and quality of the devices depends on the dielectric properties. Therefore it is critical 10 measure the dielectric properties of the material at high frequencies. especially in the microwave region. During the last decade more and more superconducting devices are available in the market. This makes the need for understanding the dielectric properties at cryogenic temperature. The goal of this paper is to review various dielectric characterization techniques implemented at the high electromagnetic frequency region. The typical dielectric properties of the material are the dielectric constant and loss tangent. The paper also will address the microwave cryogenic characterization of dielectric materials. The cryogenic microwave properties of many bulk and planar (substrate) dielectric resonator materials are\ud presented

Cryogenic microwave dielectric properties of sintered (Zr 0.8 Sn 0.2) TiO4 doped with CuO and ZnO

The effect of CuO on the sintering temperature, microstructure, and the microwave dielectric properties of (Zr0.8Sn0.2)TiO4 (ZST) has been investigated. The microwave dielectric properties of the ZST ceramics have been measured at cryogenic temperatures (15–290 K). The crystallite sizes of the sintered ZST ceramics are in the 30–50-nm range. The addition of CuO effectively reduced the sintering temperature to 1300°C due to the liquid-phase effects. The addition of CuO did not cause any secondary phases up to 1.5 wt% of CuO. It is found that the quality factor (Q) of the sample without CuO decreased with an increase in temperature, whereas the samples with the addition of CuO up to 1.0 wt% showed less dependence on temperature at cryogenic temperatures. The microwave dielectric properties of the ZST ceramics measured at cryogenic temperatures exhibited a Q factor of 15 000 for pure ZST and 11 800 for ZST with 0.5 wt% of CuO at 15 K. The increase in Q factor at cryogenic temperatures can be attributed to the reduction in both intrinsic and extrinsic losses in the ZST ceramics

Low temperature dielectric properties of Ca0.7Nd0.3Ti0.7Al0.3O3 microwave ceramics

CaTiO3-NdAlO3 based ceramic composites with the nominal composition Ca0.7Nd0.3Ti0.7Al0.3O3 was synthesized by the conventional ceramic method and the dielectric measurements were carried out as a function of frequency (1KHz-4MHz) in the temperature range of 150-303 K. The complex impedance spectroscopy (CIS) analysis has been carried out to investigate the influence of its microstructure on electrical properties as a function of temperature and frequency. Impedance studies indicated the presence of a temperature dependent relaxation process in the material with a spread of relaxation times. Microwave measurement at low temperatures reveals that these systems has a slight increase in dielectric constant as temperature decreases and a loss tangent peak around 50Kelvin

Bi2 (Zn 2/3-x/3Nb4/3-2x/3Ti x)O7 ceramics - a low temperature sintered material for LTCC applications

Ceramic samples with low sintering temperature were prepared by solid state reaction from the respective high purity oxide powders. Bi2 (Zn 2/3-x/3Nb4/3-2x/3Ti x)O7 were sintered below 900 degree Celcius and the density is above 90%. The frequency dependent dielectric properties of these ceramics up to 1MHz were measured using Agilent 4294A impedance analyser. The dielectric properties of Bi2 (Zn 2/3-x/3Nb4/3-2x/3Ti x)O7ceramics with x = 0 to 0.4 were estimated at microwave frequencies from room temperature to 15 K using Dielectric Post (DP) resonator techniques. The high dielectric permittivity together with the low sintering temperature will make this material an attractive candidate for LTCC applications

Bi2(Zn2/3-x/3Nb4/3-2x/3Tix)O7 ceramics - a high permittivity microwave dielectrics for electronics application

High-K materials are needed for many microwave applications. In this paper microwave properties of Bi₂Zn₂/₃₋ₓ/₃Nb₄/₃₋₂ₓ/₃TiₓO₇ ceramics with x of 0, 0.2 and 0.4 are presented. Ceramics samples were prepared by solid state reaction from respective high purity oxide powders. Dielectric microwave properties of synthesised materials were measured at 3 GHz in a wide range of temperatures using Dielectric Post (DP) resonator technique. The high dielectric permittivity together with low sintering temperature make M-BNZ an attractive candidate for Low Temperature Co-fired Ceramics for charge storage applications in various electronics circuits and microwave systems

Effect of CuO on the sintering and cryogenic microwave characteristics of (Zr 0.8 Sn 0.2) TiO4 ceramics

The effect of CuO on the sintering temperature, microstructure and microwave dielectric properties of (Zr0.8Sn0.2)TiO4 (ZST) modified with 1 wt% of ZnO has been investigated. Microwave dielectric properties of ZST ceramics are measured from cryogenic to room temperatures (15–290 K). Crystallite sizes of sintered ZST ceramics as derived from XRD are in the 30–50 nm range. The addition of CuO effectively reduced the sintering temperature to 1300 °C, possibly due to liquid-phase effects. Addition of CuO did not cause any secondary phases up to 1.5 wt% of CuO. The dielectric constant (epsilonr) and temperature coefficient of resonant frequency (τf) of ZST ceramics do not significantly vary with temperature, whereas the unloaded quality factor (Qu) changes noticeably. It is found that the Qu factor of the sample without CuO decreased with increase in temperature, whereas the samples with addition of CuO up to 1.0 wt% showed less dependence on temperature. The Qu factor of CuO-free ZST is 15,000 and that of ZST with 0.5 wt% of CuO is 11,800 at 15 K. The Qu factor while measured at room temperature ranged between 2900 and 7000. Efforts were made to understand whether the increase in Qu factor at both cryogenic and room temperatures is the result of intrinsic or extrinsic factors

Optical parameters induced by phase transformation in RF magnetron sputtered TiO2 nanostructured thin films

Pure TiO2 thin films were deposited onto quartz substrates using a ceramic TiO2 target at an elevated substrate temperature of 573 K by RF magnetron sputtering, and an analysis of structural, optical and photoluminescence characteristics of the films upon phase transformation is reported in this paper. Structural investigations using X-ray diffraction revealed that the as-deposited film was amorphous in nature. Thermal annealing for 2 h at 873 K in air resulted in the formation of anatase phase, and a phase transformation to rutile was observed at 1073 K. An increase in grain size and an improvement in crystallinity were also observed on annealing. Rod- like rutile crystallites were observed in the SEM images of the film annealed at 1273 K. As-deposited films and films annealed up to 1073 K were highly transparent in the visible region with a transparency >80%. Optical band gap of the films decreased upon thermal annealing which is attributed to phase transformation from amorphous to anatase and then to rutile. Optical parameters such as refractive index, optical conductivity and optical dielectric constant increased with increase in annealing temperature. Since rutile is the optically active phase, the superior refractive index of the film annealed at 1073 K along with its high transparency in visible region suggests the application of this film in antireflective coatings. Photoluminescence emission of maximum intensity was observed for the film annealed at 873 K, which exhibits anatase phase. Intense blue emission observed in this film makes it suitable for use in optoelectronic display devices