Photo-Induced Thermally Stimulated Depolarization Current (TSDC) in Natural and Synthetic Alexandrite (BeAl2O4:Cr3+)

The investigation of electrical properties in alexandrite (BeAl2O4:Cr3+) in synthetic and natural forms is presented in this paper. Alexandrite is a rare and precious mineral that changes color according to the light incident on it. In the synthetic form, it is used technologically as an active laser medium. The electrical characterization was obtained using the Thermally Stimulated Depolarization Current (TSDC) technique, an interesting tool to study the behavior of impurities in insulators. Alexandrite presented the electric dipole relaxation phenomenon, both in natural and in synthetic samples. It was possible to observe TSDC bands for the synthetic sample at around 170 K, and at around 175 K for the natural sample. Besides, photo-induced TSDC measurements were performed through the excitement of the samples by using a continuous wave argon laser. In addition, photoluminescence measurements were performed to verify in advance whether the laser light would be absorbed by the sample, and in order to complement the photo-induced TSDC measurements analysis. The results of photo-induced TSDC experiments have contributed to the understanding of the TSDC bands behavior: the results obtained with the technique suggest that there is an effective participation of Cr3+ ions in the formation of TSDC bands because they were more intense when the sample was exposed to the argon laser beam.

La_(2)O_(3)-modified BiYbO_(3)–Pb(Zr,Ti)O_(3) ternary piezoelectric ceramics with enhanced electrical properties and thermal depolarization temperature

High-performance Pb(Zr_(1−x)Ti_(x))O_(3)(PZT)piezoceramics are urgently desired by the market in view of their expanded operating temperature range,reduced property temperature dependence,and enhanced sensitivity and acoustic power.In this work,we reported a kind of low-cost and high-performance 0.06BiYbO_(3)–0.94Pb(Zr_(0.48)Ti_(0.52))O_(3) ternary piezoceramics;the modifying effects of La_(2)O_(3) on this perovskite system were investigated in terms of the structures,electrical properties,and thermal depolarization behaviors of ceramics.The field-dependent dielectric and conduction properties indicated that there are close correlations among oxygen vacancies(VO),conducting electrons,and intrinsic conduction process.The degradation in ferroelectric properties observed in those samples doped with more than 0.15 wt%of La_(2)O_(3) indicated that the occupying mechanisms of La^(3+)changed from the donor substitution for Pb^(2+)to the isovalent substitution for Bi^(3+).The thermally depoling micromechanisms of ceramics were revealed from the thermodynamic processes of defect dipoles and intrinsic dipoles within ferroelectric domains.The sample doped with 0.15 wt%of La_(2)O_(3) shows excellent electrical properties with TC=387℃,d33=332 pC/N,TKε=5.81×10^(−3)℃−1,Pr=20.66μC/cm^(2),Td=356℃.The significantly enhanced electrical properties and thermal depolarization temperature benefited from the donor substitution of La3+,decreasing the oxygen vacancy concentration in the lattice and possibly optimizing the ferroelectric domain structure of ceramics.

Effect of heating treatment on trap level distribution in polyamide 66 film electrets

The effect of heating treatment on the trap level distribution in polyamide 66 film electret is studied by thermally stimulated depolarization current （TSDC） technique. For annealed polyamide 66, there are three trap levels that respectively originate from space charge trapped in amorphous phase, interphase and crystalline phase. There is one peak that originates from space charge trapped in amorphous phase for quenched one. Using multi-point method to fit the experimental curves, the detrapping current peaks can be separated and the trap depth is obtained. The shallower trap levels trapped in amorphous phase and interphase are obviously close to the deeper trap level trapped in crystalline phase for annealed polyamide 66 as the polarization temperature increases, while the trap level distribution remains unaffected by polarization temperature for quenched one.

Linear polarization output performance of Nd:YAG laser at 946 nm considering the energy-transfer upconversion

A theoretical model of quasi-three-level laser system is developed, in which both the thermally induced depolarization loss and the effect of energy-transfer upconversion are taken into account. Based on the theoretical investigation of the influences of output transmission and incident pump power on thermally induced depolarization loss, the output performance of 946 nm linearly polarized Nd：YAG laser is experimentally studied. By optimizing the transmission of output coupler, a 946 nm linearly polarized continuous-wave single-transverse-mode laser with an output power of 4.2 W and an optical-optical conversion efficiency of 16.8% is obtained, and the measured beam quality factors are M2 = 1.13 and My2 = 1.21. The theoretical prediction is in good agreement with the experimental result.

Role of matrix phase and electric field gradient in Na_(1/2)Bi_(1/2)TiO_(3)eBaTiO_(3) :ZnO composites

Na_(1/2)Bi_(1/2)TiO_(3)-based materials exhibit potential for applications in high-power ultrasonics.The com-posites of Na_(1/2)Bi_(1/2) TiO_(3)-yBaTiO_(3)(NBTyBT;y denotes mole%)with ZnO inclusions were demonstrated to stabilize a ferroelectric equilibrium that led to enhanced thermal depolarization temperature(T_(d))and increased mechanical quality factor(Q_(m)).This work addresses the influence of the matrix NBTyBT phase by investigating two limiting choices based on symmetry(tetragonal/rhombohedral)and polar(relaxor/ferroelectric)nature.While the composites constituting the tetragonal NBT9BT(non-ergodic relaxor at room temperature)matrix phase exhibit improved T d,the critical temperatures in the composites with rhombohedral NBT3BT(displaying spontaneous ferroelectric order at room temperature)exhibit only marginal changes.Further,NBT3BT composites feature a 45%increase in Q m,while the corresponding increase is roughly three-fold for the NBT9BT composites.A 3-D Finite Element Method is used to simulate the electric field gradient at the matrix/inclusion interface,with the effective field distribution estimated to be higher than the applied field for highly conducting ZnO inclusions.The electrical properties indicate that,while the deviatoric stress at the matrix/inclusion interface stabilizes the ferroelectric equilibrium for the relaxor matrix phase,the stresses disrupt the long-range order for the ferroelectric matrix phase.These results establish the volume-limit of the second phase to stabilize a ferroelectric equilibrium,in addition to substantiating the role of residual stress evidenced by changes in the polar nature.Finally,a comparison of the composites with different NBTyBT phases is presented,with NBT6BT:ZnO composites demonstrating an optimal increase in both T_(d) and Q_(m).