Theoretical Study on the Piezoelectric Performance of Lead-Free 1–3-Type Composites

The paper is devoted to the analysis of high-performance piezo-composites based on lead-free ferroelectric single crystals. The composite consists of parallelepiped-shaped single-crystal rods which are surrounded by a laminar polymer matrix, and the composite as a whole is described by 1–2–2 connectivity. Such a composite structure promotes high piezoelectric sensitivity and hydrostatic response. Of particular interest are piezoelectric coefficients g*33 and h*33, squared figure of merit d*33 g*33, electromechanical coupling factor k*t at the thickness-mode oscillation, and hydrostatic parameters g*h and d*h g*h. The influence of the laminar matrix on the aforementioned parameters is studied in a wide volume-fraction range. Examples of maxima and large anisotropy of some effective parameters are discussed for the 1–2–2 composites based on [Lix(K1−yNay)1−x](Nb1−zTaz)O3:Mn single crystals. The role of elastic properties of the laminar matrix in achieving large hydrostatic parameters and piezoelectric anisotropy of these composites is emphasised. Their effective parameters are compared to those of composites based on the lead-containing relaxor-ferroelectric single crystals and to specific parameters of poled textured ceramics. Advantages of the studied composites over the relaxor-ferroelectric-based composites and textured ceramics open up new possibilities to apply the 1–3-type lead-free composites as active elements of piezoelectric sensors, hydrophones, energy-harvesting, and transducer devices.</p

Nanodiamond Graphitization: A Magnetic Resonance Study

We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) study of the high-temperature nanodiamond-to-onion transformation. 1H, 13C NMR and EPR spectra of the initial nanodiamond samples and those annealed at 600, 700, 800 and 1800 ° C were measured. For the samples annealed at 600 to 800 ° C, our NMR data reveal the early stages of the surface modification, as well as a progressive increase in sp2 carbon content with increased annealing temperature. Such quantitative experimental data were recorded for the first time. These findings correlate with EPR data on the sensitivity of the dangling bond EPR line width to air content, progressing with rising annealing temperature, that evidences consequent graphitization of the external layers of the diamond core. The sample annealed at 1800 ° C shows complete conversion of nanodiamond particles into carbon onions