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Pristine ZnO and Sm-doped ZnO nanoparticles were synthesized using a wet chemical co-precipitation technique. The morphological and structural characteristics of pristine and Sm-doped ZnO were studied by field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) techniques. Increases in lattice parameters, interplanar spacing, and volume was observed from the XRD patterns compared to its JCPDS card. Crystallite size, dislocation density, deformation stress, lattice strain, and energy density for both pristine and Sm-ZnO nanoparticles were calculated using Scherrer and Williamson–Hall (W–H) methods. An energy bandgap reduction was observed in the Sm-doped ZnO (Eg ~ 2.7 eV), which played a crucial role in explaining the increased leakage currents in Sm-ZnO. The Sm-doped ZnO nanoparticles exhibited a remnant polarization (Pr ~ 0.163 µC/cm2) and a coercive field (Ec ~ 25.33 kV/cm). Current–voltage (I–V) characteristics show maximum current generated on applying varying voltages (Vmax = 40 V, Imax = ~600 μA). Frequency- and temperature-dependent dielectric studies were conducted to examine the change in the values of the dielectric constant and dielectric loss with the variation in frequency and temperature. The Sm-doped ZnO-based nanogenerator generated an output voltage ~ 400 mV at tapping force of ~ 0.02 kgf, which makes it a prominent candidate for self-powered devices. [ABSTRACT FROM AUTHOR]

Ferroelectricity in pure ZnO nanocrystals is an unlikely physical phenomenon. Here, we show origin of high temperature ferroelectricity in ZnO as a result of yttrium (Y) doping. First, we briefly introduced the wet chemical synthesis of pure and yttrium (Y) doped ZnO nanocrystals. The crystalline phase and morphological appearance of as synthesized pure and Y-doped ZnO nanocrystals were examined using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. By Y-doing, the morphology of ZnO crystals evolved from 1D nanopencil (pure ZnO) to 3D flower-like architectures assembled by 2D porous nanosheets (Y-ZnO). Crystallite size, deformation stress, energy density and lattice strain of both the nanoparticles were evaluated using Scherrer and Williamson-Hall methods. Frequency as well as temperature dependence of dielectric constant, dielectric loss and ac conductivity of Y-doped ZnO nanosheets were investigated. Ferroelectricity in Y-doped ZnO nanosheets was established using the temperature dependent curve of dielectric constant and the room temperature polarization hysteresis loop. The temperature dependent curve of dielectric constant displayed a ferroelectric to paraelectric transition peak at 138 °C. The Y-ZnO nanosheets exhibit weak ferroelectric polarization hysteresis loop with a remnant polarization (Pr) of 0.09 µC/cm2 and a coercive field (Ec) of 5.87 kV/cm (@ RT). The nature of the leakage present in Y-ZnO sample was extracted from the time-dependent compensasted (TDC) hysteresis study. Leakage current density was found to decrease due to Y-doping in ZnO nanocrystals. [ABSTRACT FROM AUTHOR]

Gadolinium doped ZnO nanorods were grown by wet chemical method. Line broadening of each diffraction peak was studied to evaluate the crystallite size, lattice strain, stress and energy density. Crystallite size was estimated by Scherrer and Williamson-Hall methods. The size was found to be in good agreement with the results of transmission electron microscopy. As a result of Gadolinium doping, high remnant polarization (P r = 0.29 μC/cm 2 ) and coercive field (E c = 16.41 kV/cm) were observed. The decrease in leakage current due to Gadolinium doping makes ZnO a remarkable candidate for ferroelectric capacitor. High ferroelectric phase transition temperature (T c = 215 °C) and large piezoelectric coefficient (d 33 = 45.49 pm/V) were observed which makes Gadolinium doped ZnO sample useful for high temperature non-volatile ferroelectric memory applications. [ABSTRACT FROM AUTHOR]

Pure and Sb-doped 0.64PMN-0.36PT (PMN-PT) ceramics near MPB have been prepared using columbite precursor technique. The effects of Sb-doping on microstructure and electrical properties were studied systematically. Powder XRD and SEM exhibited the formation of pure perovskite phase with homogeneous microstructure. As compared to the pure PMN-PT ceramics, enhanced dielectric constant, and reduced transition temperature (T) and dielectric loss (tan δ) were observed for Sb-doped PMN-PT ceramics. Displacement-Voltage (D-V) butterfly hysteresis loops and quasi-static d meter revealed a higher value of piezoelectric charge coefficient (d) for Sb-doped sample (644 pm/V and 551 pC/N) as compared to pure ceramic (435 pm/V and 410 pC/N). P-E hysteresis curves showed improved ferroelectric properties after Sb doping. A high value of pyroelectric coefficient (p ∼ −1170.4 µC m °C) for Sb-doped PMN-PT ceramic was obtained. Sb-doped PMN-PT ceramic showed an excellent anti-fatigue nature over 10 switching cycles. Small leakage current was evident from J-E analysis for both the ceramics. Therefore, Sb-doped PMN-PT ceramic proved to be a better choice for applications in the electronic ceramic industries. [ABSTRACT FROM AUTHOR]

The observation of feeble ferroelectricity and giant piezoelectricity in doped II–VI ZnO binary semiconductor has inspired a great deal of research interest, which could pave the way to reduce the toxic effects on the environment, and to develop small molecule ferroelectrics and flexible piezoelectric nanogenerator. The main challenge for practical application of the ZnO is the attainment of a high Curie temperature to be compatible with junction temperatures. This review focuses primarily on the piezoelectric and ferroelectric properties of zinc oxide (ZnO) nanostructures. One of the desirable outcomes is to provide a useful insight into various processes which may induce ferroelectricity and enhance piezoelectricity in non-ferroelectric and weak piezoelectric ZnO. Taking into consideration the recent progress in this area, topics such as local switchable polarization, effects of defects, ionic charge of the dopant and ionic size of the dopant, and their contributions to piezoelectric and ferroelectric properties of ZnO are discussed. A critical review of the question dealing with the origin of ferroelectricity in ZnO is given. In a similar vein, methods for enhancing piezoelectric coefficient of ZnO are briefly discussed, followed by their applications in potential devices. From this review, it can be concluded that ZnO (a lead-free and biocompatible material) on being doped with suitable dopants show king-sized piezoelectric response and feeble ferroelectric response, which possibly make ZnO an attractive alternative to lead based perovskites for specific applications. This subject is of current interest to various scientists worldwide and hence, motivated us to write a review article with an aim that it would give further momentum to the scientists already working in this field. Image 1 • A comprehensive review on piezoelectric and ferroelectric properties of ZnO nanostructure. • Research of the past 30 years from nearly 50 research groups are reviewed with over 225 references. • Described strategies to obtain gigantic piezoelectric response and feeble ferroelectricity. • Potential of piezoelectric ZnO as an environmental friendly energy harvester is established. • Expected to be a handy guide for young researcher in the field of versatile ZnO. [ABSTRACT FROM AUTHOR]

Abstract Pure and Neodymium (Nd) doped ZnO nanorods were prepared using cost effective wet chemical co-precipitation method and used for the fabrication of flexible piezoelectric nanogenerator. The structure and morphology of ZnO and Nd-ZnO samples were studied using powder X-ray diffraction, FESEM and TEM techniques. Ferroelectric measurements showed a remanent polarization (P r) of ∼0.064 μC/cm2 and coercive field (E c) of ∼6.04 kV/cm, respectively at 600 V. Leakage current density was found to be reduced after Nd doping in ZnO nanorods. Enhanced Curie temperature (T c = 125 °C) and large piezoelectric coefficient (d 33 = 512 pm/V) were observed in Nd doped ZnO nanorods, which makes Nd-ZnO a better candidate for piezoelectric energy harvesting and high temperature nano-storage devices. Moreover, flexible piezoelectric nanogenerators (PENGs) were fabricated using ZnO and Nd-ZnO nanorods. The Nd-doped ZnO based NG showed high piezoelectric performance by generating average voltage of ∼31 V under finger tapping (∼0.3 N), which was more pronounced in comparison to ZnO based NG (∼2 V). Graphical abstract Image 1 Highlights • Pure and Nd-doped ZnO NRs were synthesized via co-precipitation method. • Piezo-/di-/ferroelectric properties for Nd-ZnO were reported. • Giant piezoresponse for Nd-ZnO NRs (512 pm/V) from the D-V butterfly loop. • Flexible pure and Nd-doped ZnO based PENGs were successfully fabricated. • An ultra-sensitive response (∼31 V) from Nd-ZnO based NG was obtained. [ABSTRACT FROM AUTHOR]