Large pyroelectric properties at reduced depolarization temperature in A-site nonstoichiometry composition of lead-free 0.94NaxBiyTiO3–0.06BazTiO3 ceramics

Nonstoichiometry lead-free 0.94NaxBiyTiO3–0.06BazTiO3 (NxByT–0.06BzT) (from x = y = 0.5, z = 1.00 to x = 0.5, y = 0.534, z = 1.02) ceramic compositions were prepared by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. The depolarization temperature (Td) can be lowered by modifying x, y and z. The pyroelectric coefficient (p) of nonstoichiometry NxByT–0.06BzT compositions is greatly increased, compared with stoichiometry NBT–0.06BT composition, from 3.15 × 10−4 C m−2 °C−1 at room temperature (RT) and 23.9 × 10−4 C m−2 °C−1 at Td, and reaches maxima of 6.99 × 10−4 C m−2 °C−1 at RT and 75.3 × 10−4 C m−2 °C−1 at Td for x = y = 0.52 and z = 1. The figures of merits, Fi, Fv, and FD, also have been improved from 1.12 × 10−10 m v−1 and 0.021 m2 C−1 to 2.50 × 10−10 m v−1, 0.047 m2 C−1 and 16.63 × 10−6 Pa−1/2, respectively, for N0.52B0.52T–0.06BT composition at RT. Furthermore, N0.52B0.52T–0.06BT composition shows a huge enhancement in Fi, Fv and FD to 26.9 × 10−10 m v−1, 0.39 × 10−10 m2 C−1 and 138.7 × 10−6 Pa−1/2, respectively, at Td. The same composition also presents FC values which are ~2.58 and ~2.86 (×10−9 C cm−2 °C−1) at RT at 100 and 1000 (Hz). N0.5B0.534T–0.06BT and N0.5B0.534T–0.06B1.02T compositions show a large p values at a wide temperature range. The enhanced pyroelectric properties make nonstoichiometry N0.52B0.52T–0.06BT composition a promising candidate for pyroelectric and other applications at wide temperatures range

Determinants of corporate cash holdings: An empirical study of Chinese listed firms

This study explores the determinants of corporate cash holdings in the Chinese context. As one of the largest developing countries in the world, China offers an interesting opportunity to explore the role of corporate governance, and ownership structure in explaining corporate cash holdings. Owing to the unique economic problems in the developing and emerging economies, this study aims to investigate whether the research findings on developed countries could be generalized globally. Applying fixed-effects estimations on a sample of 115 Chinese firms listed between 2012 and 2016, we find that the level of corporate cash holdings has a significantly negative relationship with leverage, bank debt, non-cash liquid assets and managerial ownership. In particular, cash flow volatility, investment opportunity and dividend have a significantly positive relationship with cash holdings levels. These findings are consistent with the majority of the existing studies carried out in the Western context. We also find that firm size, cash flow, board independence and ownership concentration have a significant influence on the level of corporate cash holdings. Our study contributes to the finance literature and we offer new insights into the relationship between corporate governance and corporate cash holdings in the Chinese context. Some of the findings on the developed countries could be generalized to a wider context. Further, the unique relationship between corporate governance and cash holdings in the Chinese context provides empirical insights for further research

The effects of Ba2+ content on depolarization temperature and pyroelectric properties of lead-free 0.94Na0.5Bi0.5TiO3-0.06Ba1+xTiO3 ceramics

Lead-free 0.94Na0.5Bi0.5TiO3–0.06Ba1+xTiO3 (NBT–0.06B1+xT) ceramics (0.0 ≤ x ≤ 0.03) were synthesized by a conventional solid-state reaction process. X-ray diffraction shows that the compositions are at the morphotropic phase boundary where rhombohedral and tetragonal phase coexist. Grain size slightly changes with the increase of Ba2+ content and reaches the minimum at x = 0.02. The depolarization temperature (Td) decreases with the extra Ba2+content but the lowest Td was obtained at x = 0.01–0.02. The pyroelectric coefficient (p) was measured as a function of Ba2+ content, and increased from 2.90 × 10−4 to 3.54 × 10−4 C m−2 °C−1, and from 55.3 × 10−4 to 740.7 × 10−4 C m−2 °C−1 for x = 0.00 and 0.02 at RT, and depolarization temperature (Td) respectively. The pyroelectric coefficient (p) shows a large increase with rising the temperature and reaches the maximum value at the depolarization temperature (Td). The figures of merits of Fi, Fv and FD have all been improved with the addition of extra barium. These improved pyroelectric properties indicate that NBT–0.06B1+xT is a promising material for pyroelectric applications or a wide range of temperature

The decrease of depolarization temperature and the improvement of pyroelectric properties by doping Ta in lead-free 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics

Ta-doped lead-free 0.94NBT-0.06BT-xTa (x=0.0–1.0%) ceramics were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. The depolarization temperature (Td) shifted to lower temperature with the increase of Ta content. The pyroelectric coefficient (p) of doped ceramics greatly enhanced compared with undoped material and reached a maximum of 7.14×10−4 C m−2 °C−1 at room temperature (RT) and 146.1×10−4 C m−2 °C−1 at Td at x=0.2%. The figure of merits, Fi and Fv, also showed a great improvement from 1.12×10−10 m v−1 and 0.021 m2 C−1 at x=0.0 to 2.55×10−10 m v−1 and 0.033 m2 C−1 at x=0.2% at RT. Furthermore, Fi and Fv show the huge improvement to 52.2×10−10 m v−1 and 0.48×10−10 m v−1 respectively at Td at x=0.2%. FC shows a value between 2.26 and 2.42 ×10−9 C cm−2 °C−1 at RT at x=0.2%. The improved pyroelectric properties make NBT-0.06BT-0.002Ta ceramics a promising infrared detector material

Enhancement of pyroelectric properties of lead-free 0.94 Na 0.5 Bi 0.5 TiO 3-0.06 BaTiO 3 ceramics by La doping

Lead-free 0.94NBT-0.06BT-xLa ceramics at x = 0.0–1.0 (%) were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. With increasing La3+ content pyroelectric coefficient (p) and figures of merits greatly increase; however, the depolarization temperature (Td) decreases. p is 7.24 × 10−4C m−2 °C−1 at RT at x = 0.5% and 105.4 × 10−4C.m−2 °C−1 at Td at x = 0.2%. Fi and Fv show improvements at RT from 1.12 (x = 0%) to 2.65 (x10 −10 m v−1) (x = 0.5%) and from 0.021 to 0.048 (m2.C−1) respectively. Fi and Fv show a huge increase to 37.6 × 10−10 m v−1 and 0.56 m2 C−1 respectively at Td at x = 0.2%. FC shows values of 2.10, 2.89, and 2.98 (x10−9C cm−2 °C−1) at RT at 33, 100 and 1000 (Hz) respectively. Giant pyroelectric properties make NBT-0.06BT-xLa at x = 0.2% and 0.5% promising materials for many pyroelectric application

Giant pyroelectric properties in La and Ta co-doped lead-free 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics

La and Ta co-doped Lead-free 0.94NBT-0.06BT ceramics were synthesized by a conventional solid-state route. The compositions remain at a morphotropic phase boundary. The depolarization temperature (Td) decreased with increasing doping contents. The room temperature (RT) pyroelectric coefficient (p) was highly enhanced compared with undoped material (3.15 × 10−4 C m−2 °C−1) and reached 12.9 × 10−4 C m−2 °C−1, whereas, at Td, 58.6 × 10−4 C m−2 °C−1 could be obtained rather than 23.9 × 10−4 C m−2 °C−1 for undoped materials. The pyroelectric figure of merits, Fi and Fv, also showed a huge improvement from 1.12 × 10−10 m v−1 and 0.021 m2 C−1 of undoped material to 4.61 × 10−10 m v−1 and 0.078 m2 C−1 of doped materials at RT, and to 20.94 × 10−10 m v−1 and 0.28 × 10−10 m2.C−1 at Td. RT FC values are ∼2.40, 2.46, and 2.57 (×10−9 C cm−2 °C−1) at frequency 33, 100 and 1000 (Hz) respectively, at La = Ta = 0.2%. The pyroelectric coefficient achieved at RT in this study is almost one order of magnitude higher than PZT materials, furthermore, the figure of merits of the new compositions are comparable with or even better in those of PZT materials and other lead-free ceramics. The improvement in the pyroelectric properties makes La and Ta co-doped NBT-0.06BT ceramics possible materials to replace lead-containing PZT ceramics for infrared detector materials at a wide temperature range