Pr-doped ZnO Research Articles

Synthesis of Pr-doped ZnO nanospindles by one-pot precipitation as a triethylamine sensor

The development of high performance triethylamine (TEA) sensors for the protection of human safety is essential. Herein, we reported a promising semiconductor metal oxide (SMO) gas sensor based on Pr-doped ZnO nanospindles as the sensing materials for the detection of TEA. The elemental composition and micromorphology of the as-prepared samples were systematically analyzed. The gas sensing performance of the pristine, 1 mmol%, 2 mmol%, and 3 mmol% Pr-ZnO sensor was evaluated. Among them, the 2 mmol% Pr-ZnO sensor exhibited the highest response value for TEA gas, and reached 158.0 towards 50 ppm TEA at 200 °C, which was about 10.0-fold higher than the response value of the pristine ZnO sensor. In addition, the 2 mmol% Pr-ZnO sensor also showed good reproducibility, rapid response/recovery time (10/46 s), theoretical limit of detection (168 ppb), outstanding long-term stability, and excellent selectivity for TEA gas.

Synthesis, Analysis and Visible-Light-Driven Photocatalysis of 0–5% Pr-Doped ZnO Nanoparticles

Synthesis, Analysis and Visible-Light-Driven Photocatalysis of 0–5% Pr-Doped ZnO Nanoparticles

Improved acetone sensing performance of Pr6O11-loaded ZnO nanorods

To improve the acetone sensing performance of ZnO nanorods, Pr-doped ZnO nanorods were prepared by a hydrothermal method and characterized by XRD, SEM and XPS. The results indicate that the Pr dopant existed in the form of Pr6O11 nanoparticles covering the ZnO nanorods. Among all sensors with the mole ratio of Pr/Zn as 0, 0.03, 0.05 and 0.1, the Pr6O11-loaded ZnO sensor with Pr/Zn as 0.05 exhibited the highest gas response (47.7) to 100 ppm acetone with relatively high repeatability, stability and selectivity at the prime working temperature of 190 °C. The improved sensing performance can be ascribed to the larger electron depletion region and higher Schottky barrier height in the ZnO nanorods caused by the electron transfer from ZnO to Pr6O11 across the Pr6O11/ZnO interface.

Resistive switching behavior and optical properties of transparent Pr-doped ZnO based resistive random access memory

Pr-doped ZnO thin films (Zn1−xPrxO) (x = 0.00, 0.01, 0.02, 0.04) were prepared on fluorine-doped tin oxide substrates by means of the sol–gel method and spin coating technology, followed by rapid thermal annealing treatment at 800 °C. The influence of Pr content on the structural and optical properties of the Zn1−xPrxO thin film was examined and discussed. The wurtzite hexagonal structural characteristics were investigated by X-ray diffraction analysis, and Pr3+ substitution for Zn2+ ions was indicated. Finally, the typical bipolar current-voltage switching curves and electrical conduction model of Zn1−xPrxO film resistive random access memory devices were discussed and investigated for low resistance state/high resistance state in the initial forming process.

Facile synthesis of Pr-doped ZnO photocatalyst using sol–gel method and its visible light photocatalytic activity

In the present research, pristine ZnO and praseodymium (Pr)-doped ZnO (Pr0.02Zn0.98O,Pr0.04Zn0.96O) nanoparticles were synthesized using sol–gel method for photocatalytic degradation of methyl orange (MO) dye under visible light illumination. The structure of the designed nanoparticles was shown by XRD to be hexagonal wurtzite structure with no spurious peaks. The EDS was used to authenticate the existence of dopant with elemental composition. Enhanced optical absorption in the visible region was observed by DRS study. The photocatalytic test revealed that Pr0.04Zn0.96O demonstrated the excellent photocatalytic performance for MO degradation under visible light illumination. Electrochemical impedance spectroscopy under visible light illumination verified the increased photocatalytic activity of Pr0.04Zn0.96O photocatalyst. These results identify that introduction of Pr-doped ZnO nanoparticles enhanced the visible light active degradation activity due to inhibition of electron–hole recombination, thereby enhancing the optical response of ZnO to visible region.

Microstructural analysis, dielectric properties and room temperature magnetic ordering of Pr-doped ZnO nanoparticles

Praseodymium (Pr ion)-doped zinc oxide nanoparticles (Zn1−xPrxO, x = 0.00, 0.02, 0.05) were prepared by chemical co-precipitation method. The as-dried samples were annealed at 400 °C for 6 h duration in vacuum (10−2 mm of Hg). Crystallographic phase formation of each prepared sample is determined by matching the peak positions of the observed X-ray diffractograms with those of JCPDS file no. 76-0206. Rietveld refinement of the XRD data is also carried out to confirm the desired crystallographic phase. Analysis of FTIR spectroscopic data confirms that no unwanted chemical bonding related to impurity is present in the sample. Intrinsic defects are investigated by observing photoluminescence spectroscopy of each sample. Due to the presence of bound magnetic polaron interaction mediated by defects like oxygen vacancy and zinc vacancy, both 2 and 5% Pr-doped ZnO nanoparticles show unsaturated hysteretic magnetization versus magnetic field loop at room temperature along with the presence of paramagnetic contribution. The presence of paramagnetic and ferromagnetic contribution confirmed from the nature of variation of magnetization vs. temperature curves. Dielectric measurements of each sample show that the substitution of dopant enhances the dielectric constant of the host system of ZnO and reduces the dielectric loss. AC electrical conductivity of the doped sample is lowered compared to that of ZnO which indicates that the doped samples would be useful for dielectric applications. The improved magnetic and dielectric properties of the doped samples open a new area for application in spintronic device as dilute magnetic dielectric.

Nanoindentation and nanoscratch behavior of ZnO:Pr thin films deposited by DC sputtering

Abstract

Synthesis of Pr-doped ZnO nanoparticles: Their structural, optical, and photocatalytic properties**Project supported by the International Cooperation Program of the Ministry of Science and Technology of China (Grant No. 2015DFR00720), the Cooperation Program of Wuhan Science and Technology Bureau, China (Grant No. 2016030409020219), and the Shenzhen Committee on Science and Technology Innovation, China (Grant No. JCYJ20170818112901473).

Undoped and praseodymium-doped zinc oxide (Pr-doped ZnO) (with 2.0-mol%–6.0-mol% Pr) nanoparticles as sunlight-driven photocatalysts are synthesized by means of co-precipitation with nitrates followed by thermal annealing. The structure, morphology, and chemical bonding of the photocatalysts are studied by x-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive x-ray emission spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), respectively. The optical properties are studied by photoluminescence (PL) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). We find that Pr doping does not change the crystallinity of ZnO; but it reduces the bandgap slightly, and restrains the recombination of the photogenerated electron–hole pairs. The photocatalytic performance of the photocatalysts is investigated by the photodegradation reaction of 10-mg/L rhodamine B (RhB) solution under simulated sunlight irradiation, showing a degradation rate of 93.75% in ZnO doped with 6.0-mol% Pr.

Photoluminescence quenching and photocatalytic enhancement of Pr-doped ZnO nanocrystals

This work reports the synthesis of novel praseodymium (Pr)-doped ZnO nanocrystals with excellent photocatalytic activity through modified solid-state reaction route. The impacts of doping on the wurtzite hexagonal structure are analysed with X-ray diffraction (XRD) and Raman spectroscopy. The production of defect levels and the formation of Urbach energy within the system are confirmed using photoluminescence (PL) techniques and UV/Vis diffuse reflectance spectroscopy, respectively. The linear relationship between Urbach energy and band gap energy is elucidated from UV/Vis spectroscopy analysis. The changes happened to morphology by doping were tackled using scanning electron microscopy (SEM). The concentration quenching effect of PL emission with Pr doping is explained in detail. A three-fold enhancement in the photocatalytic activity was achieved with optimum Pr incorporation in ZnO. This work successfully correlated PL quenching and enhanced photocatalytic activity with the defect production happened in ZnO system on Pr doping. The practical applicability of the photocatalyst was confirmed with a stability test.

Unipolar resistive switching properties of Pr-doped ZnO thin films

Abstract Pr-doped ZnO hexagonal structure thin films with c-axis preferred orientation were deposited on Pt/Ti/SiO 2 /Si substrates by chemical solution deposition technique. The effects of Pr doping amount on the resistive switching behavior of Pt/Zn 1−x Pr x O/Pt (x = 0, 0.01, 0.03, and 0.05) memory cells were investigated. The results showed that Pr-doping lowered the c-axis orientation degree of the ZnO thin films, but improved the resistive switching properties of Pt/Zn 1−x Pr x O/Pt devices. The resistive switching devices exhibited good endurance, long retention, and uniform switching voltages. I-V characteristics and their temperature dependence analysis indicated that the conduction mechanism of LRS was Ohmic behavior, and that of HRS at relatively higher voltage is trap-controlled space charge limited current. The physical origin of the resistive switching can be referred to the formation and rupture of the oxygen vacancies related filaments.

Photocatalytic treatment of aqueous solutions at high dye concentration using praseodymium-doped ZnO catalysts

In this work the photocatalytic activity of Pr-doped ZnO (Pr-ZnO) photocatalysts has been addressed for the first time in the treatment of aqueous solutions at high concentration of organic dyes under UV or visible light irradiation. Pr-ZnO photocatalysts were prepared by a precipitation method. The catalysts have been characterized by different techniques such as X-ray diffraction (XRD), UV–Vis diffuse reflectance (UV–Vis DRS) and Raman spectroscopy. XRD results showed that Pr3+ ions were successfully incorporated into the ZnO lattice. UV–Vis DRS spectra evidenced that Pr-ZnO samples present band-gap values of about 3.0eV, lower than undoped ZnO (3.3eV). The efficiency of photocatalysts has been tested in the photocatalytic removal of the azo dye Eriochrome Black T (EBT) under UV or visible light irradiation. The experimental results showed that the values of discoloration and mineralization rate are correlated to the Pr doping level, evidencing that the optimal loading of Pr in the ZnO structure is 0.46mol%. The influence of process parameters (catalyst dosage, initial dye concentration and presence of carbonate ions) on the extent of photocatalytic performances has been investigated. The efficiency of the optimized photocatalyst was also evaluated in the photocatalytic treatment of aqueous solutions containing the triphenylmethane Patent Blue V (PB) dye and in the treatment of a solution containing simultaneously the two selected dyes (EBT and PB). Photocatalytic activity tests in presence of ion scavengers (carbonate ions) showed that the formulated Pr-ZnO photocatalyst is not subjected to deactivation phenomena. At last, a very interesting result was observed for the treatment of a real wastewater containing Basic Red 51 dye, showing that the complete discoloration and mineralization was achieved.

B21-O-12Structure unit behavior in Pr-doped ZnO [0001] symmetric tilt grain boundaries

B21-O-12Structure unit behavior in Pr-doped ZnO [0001] symmetric tilt grain boundaries

Influence of Pr Doping on the Structural, Morphological, Optical, Luminescent and Non-linear Optical Properties of RF-Sputtered ZnO Films

The effects of Pr doping on the structural, morphological, optical and non-linear optical properties have been investigated. X-ray diffraction and Raman analysis reveals the formation of highly c-axis-oriented films with hexagonal wurtzite structure of ZnO. Atomic force microscopy and scanning electron microscopy images reveal the formation of grains with well-defined grain boundaries. The Pr-doped films present excellent optical transparency in the visible region. The photoluminescence spectra show both UV and visible emissions and the intensity of the visible emission increases with Pr doping. Nonlinear optical properties of the Pr-incorporated ZnO nanostructures have been investigated using the open aperture Z-scan technique. It is interesting to note that 1 wt.% praseodymium-incorporated ZnO film shows saturable absorption, whereas the 5 wt.% praseodymium-incorporated ZnO shows reverse saturable absorption and the high value of non-linear absorption coefficient (β) for 5 wt.% Pr-doped ZnO film suggests the suitability of these films for optoelectronic device applications.

Synthesis of Pr-doped ZnO nanoparticles by sol–gel method and varistor properties study

Pure and Pr-doped ZnO (0.5at%, 1at%,1.5at% and 2at%) nanoparticles are synthesized by sol–gel method and annealed at 500°C for 2h. The as-synthesized nanoparticles are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The samples exhibited hexagonal ZnO lattice structure and another Pr6O11 phase was detected in the 2at% Pr-doped ZnO nanoparticles. The calculated average crystalline size decreases from 29.73nm to 25.5nm when Pr content increased from 0 to 2at%. The energy dispersive X-ray spectroscopy (EDS) analysis for 2at% Pr-doped ZnO confirms the evidence of Pr in ZnO nanoparticles, and the varistor ceramics has a sintered density of 5.42g/cm3 corresponding to 96.8% of its theoretical density, with breakdown voltage of 4380V/cm and nonlinear coefficient of 16.5.

Sonochemical synthesis of Pr-doped ZnO nanoparticles for sonocatalytic degradation of Acid Red 17

Undoped and Pr-doped ZnO nanoparticles were prepared using a simple sonochemical method, and their sonocatalytic activity was investigated toward degradation of Acid Red 17 (AR17) under ultrasonic (US) irradiation. Synthesized nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. The extent of sonocatalytic degradation was higher compared with sonolysis alone. The decolorization efficiency of sonolysis alone, sonocatalysis with undoped ZnO and 5% Pr-doped ZnO was 24%, 46% and 100% within reaction time of 70min, respectively. Sonocatalytic degradation of AR17 increased with increasing the amount of dopant and catalyst dosage and decreasing initial dye concentration. Natural pH was favored the sonocatalytic degradation of AR17. With the addition of chloride, carbonate and sulfate as radical scavengers, the decolorization efficiency was decreased from 100% to 65%, 71% and 89% at the reaction time of 70min, respectively, indicating that the controlling mechanism of sonochemical degradation of AR17 is the free radicals (not pyrolysis). The addition of peroxydisulfate and hydrogen peroxide as enhancer improved the degradation efficiency from 79% to 85% and 93% at the reaction time of 50min, respectively. The result showed good reusability of the synthesized sonocatalyst.

Atomistic structure and segregation behavior in secondary structure and facet of Pr-doped ZnO Σ13 27.8° [0001] tilt grain boundary

Atomistic structure and segregation behavior in secondary structure and facet of Pr-doped ZnO Σ13 27.8° [0001] tilt grain boundary

Characterization of electrospun Pr-doped ZnO nanostructure for acetic acid sensor

Pure and Pr-doped (2wt%, 8wt%) ZnO nanostructures are synthesized by an electrospinning method and followed by calcination. The as-synthesized nanostructures are characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and static gas sensor testing device. Pure and Pr-doped ZnO nanostructure exhibited hexagonal ZnO lattice structure and another Pr7O12 phase is detected in the 8wt% Pr-doped ZnO nanofibers. The surface morphology of pure ZnO and 8wt% Pr-doped ZnO is nanofiber linked by nanosized ZnO grains. The surface morphology of 2wt% Pr-doped ZnO is spherical nano-ZnO crystal-like island. Comparing with pure ZnO nanofibers, Pr-doped ZnO nanostructure exhibit improved acetic acid sensing properties at 380°C. 8wt% Pr-doped ZnO nanofiber shows a high selectivity in detecting acetic acid, acetone and methanal. Pr-doped ZnO sensors show different optimal operating temperature with different concentration of Pr.

Nano/sub-nano analysis based on high resolution transmission electron microscopy for ceramic materials

Grain boundaries, interfaces and surfaces are very attractive areas from the viewpoint of lattice discontinuity. Doped elements and point defects often segregate there, which largely changes bulk properties such as microstructure, mechanical strength, electrical conductivity. To understand the details of the dopant effects, it is necessary to use nano-scale analysis techniques based on transmission electron microscopy with energy dispersive X-ray spectroscopy and electron energy-loss spectroscopy with nano/sub-nano electron probe. This review contains some nano-scale analysis studies performed in our research group for the grain size control of BaTiO3 polycrystals, electrical properties across single grain boundaries of n-type BaTiO3, SrTiO3 and ZnO, interface structural change of WC–Co based cemented carbides and the preparation of novel dislocation nano-wires. Grain boundaries in BaTiO3 sinters were revealed to exhibit grain boundary faceting by doping a very small amount of excess TiO2. The formation of the facets due to extra Ti–O2 bonding is closely related to abnormal grain growth, which is often observed in TiO2-excess BaTiO3 sinters. A similar faceting feature is also observed in VC-doped WC–Co cemented carbides. Doped VC strongly segregates to WC/Co interfaces to form micro facets. The formation of the micro facets resulted in WC grain size reduction. In ZnO boundaries, doped Pr was revealed to segregate at the grain boundary. The segregated Pr ions are situated in specific atomic columns. Further, electron energy-loss spectroscopy has revealed that the valence of the segregated Pr ions is 3+, which means that they are not acceptors but donors to ZnO. The improvement of varistic effect observed in Pr-doped ZnO is closely related to Zn vacancies enhanced by Pr doping. Meanwhile, dislocations are a kind of one-dimensional lattice defect including extra half planes. By pipe-diffusion of dopants at dislocation cores, we can successfully develop conducting nano-wires in insulating sapphire crystals.

Effect of Pr doping on the structural and optical properties of ZnO nanorods

Influence of Pr doping on the structural, optical properties of ZnO nanorods prepared through an aqueous solution route has been made. The wurtzite crystal structure of the host specimen was studied to be unaltered on Pr substitution into the host lattice, from the X-ray diffraction measurements. The lattice constants for the Pr-doped ZnO nanorods were observed to increase slightly with respect to the Pr composition. The morphology and chemical composition of the nanorods were studied using field emission scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and inductive coupled plasma (ICP) techniques. The high resolution transmission electron microscopy and selected area electron diffraction pattern revealed the highly crystalline nature of Pr-doped ZnO nanorods. Zn–O bonding studied from the FT-IR spectroscopy has been observed to shift towards the lower wavenumbers on Pr incorporation. The crystallinity of the nanorods has been additionally studied using Raman spectroscopy, with the sharp peak observed at 438 cm−1. A red shift in the NBE emission has been observed at 394 nm on Pr doping, along with a broad visible emission in the luminescence spectra.

Positive temperature coefficient resistor behavior in praseodymium-doped ZnO (0001¯)∣(0001¯) boundaries

Clear positive temperature coefficient resistor (PTCR) dc behavior has been shown in Pr-doped ZnO (0001¯)∣(0001¯) bicrystals by electrical characterization over an unprecedentedly wide temperature range between 40 and 1070 K. With subtraction of the PTCR dc, the admittance can be described by a deep trap level at 0.26 eV but no clue to the origin of the PTCR behavior is provided. Capacitance-voltage characteristics revealed a maximum in the Schottky barrier heights consistent with the PTCR behavior. The PTCR behavior in Pr-doped ZnO c-axis oriented bicrystals is thus phenomenologically analogous to that of the ferroelectric BaTiO3.