Intrinsic polarization and resistive leakage analyses in high performance piezo-/pyroelectric Ho-doped 0.64PMN-0.36PT binary ceramic

BaHf0.05Ti0.95O3 Ceramics from Sol-Gel and Solid-State Processes: Application to the Modelling of Piezoelectric Energy Harvesters

A typical piezoelectric energy harvester is a bimorph cantilever with two layers of piezoelectric material on both sides of a flexible substrate. Piezoelectric layers of lead-based materials, typically lead zirconate titanate, have been mainly used due to their outstanding piezoelectric properties. However, due to lead toxicity and environmental problems, there is a need to replace them with environmentally benign materials. Here, our main efforts were focused on the preparation of hafnium-doped barium titanate (BaHfxTi1-xO3; BHT) sol-gel materials. The original process developed makes it possible to obtain a highly concentrated sol without strong organic complexing agents. Sol aging and concentration can be controlled to obtain a time-stable sol for a few months at room temperature, with desired viscosity and colloidal sizes. Densified bulk materials obtained from this optimized sol are compared with a solid-state synthesis, and both show good electromechanical properties: their thickness coupling factor kt values are around 53% and 47%, respectively, and their converse piezoelectric coefficient d33∗ values are around 420 and 330 pm/V, respectively. According to the electromechanical properties, the theoretical behavior in a bimorph configuration can be simulated to predict the resonance and anti-resonance frequencies and the corresponding output power values to help to design the final device. In the present case, the bimorph configuration based on BHT sol-gel material is designed to harvest ambient vibrations at low frequency (<200 Hz). It gives a maximum normalized volumetric power density of 0.03 µW/mm3/Hz/g2 at 154 Hz under an acceleration of 0.05 m/s2.

Samarium-Doped Lead Magnesium Niobate-Lead Titanate Ceramics Fabricated by Sintering the Mixture of Two Different Crystalline Phases

The fabrication method plays a key role in the performance of lead magnesium niobate-lead titanate-based ceramics. (1 - w)[Pb(Mg1/3Nb2/3)0.67Ti0.33O3]-w[Pb1-1.5xSmx(Mg1/3Nb2/3)yTi1-yO3] piezoelectric ceramics were prepared by sintering the mixture of two different crystalline phases in which two pre-sintered precursor powders were mixed and co-fired at designated ratios (w = 0.3, 0.4, 0.5, 0.6). The X-ray diffraction results show that all the ceramics presented a pure perovskite structure. The grains were closely packed and the average size was ~5.18 μm based on observations from scanning electron microscopy images, making the ceramics have a high density that is 97.8% of the theoretical one. The piezoelectric, dielectric, and ferroelectric properties of the ceramics were investigated systematically. It was found that the properties of the ceramics were significantly enhanced when compared to the ceramics fabricated using the conventional one-step approach. An outstanding piezoelectric coefficient d33 of 1103 pC/N and relative dielectric permittivity ε33/ε0 of 9154 was achieved for the ceramics with w = 0.5.

Perovskite SrZrO3:Ho3+ phosphors: synthesis, structure, Judd-Ofelt analysis and photoluminescence properties

A series of SrZrO3:xHo3+ (x = 0.01, 0.03, 0.05, 0.07, 0.09, and 0.11 mol) perovskite phosphors have been synthesized by using the sol-gel technique. The structural and optical characteristics of the prepared phosphors have been investigated through powder XRD, FT-IR, UV-visible diffuse reflectance, and photoluminescence analysis. The photoluminescence emission spectra showed a bright characteristic peak at 545 nm (5F4 + 5S2 → 5I8) under the 454 nm excitation, which exhibits emission in the green region of the electromagnetic spectrum. The emission intensity of the phosphors starts decreasing slowly beyond 3 mol% Ho3+ ions concentration due to concentration quenching, which is attributed to the dipole-dipole interaction between Ho3+ ions. The site symmetry of the Ho3+ ions has been studied by estimating the relative Judd-Ofelt intensity parameters (Ωλ, where λ = 2, 4, 6) from the photoluminescence excitation spectrum of the SrZrO3:0.03Ho3+ phosphor. The obtained findings suggest that the synthesized phosphors will be favorable for their bright green emission and thus, can be widely used for different optoelectronic applications.