Magnetic Properties of Zn1?x Ni x O (0.25≤x≤ 0.50) Prepared by Solid-State Reactions

In this study the origin of ferromagnetism in ZnO-based bulk systems has been investigated using Ni-doped ZnO samples, Zn_1−x Ni _x O with 0.25≤x≤0.50, prepared by solid-state reactions. The structural characterizations indicated that the Ni²⁺ ions almost uniformly distributed in all the samples, and the samples have hexagonal wurtzite structure; however, when x is increased toward 0.50, a new NiO phase is formed. A ferromagnetism (FM) has been observed for all the samples at and below the room temperature. In other words, the room temperature results of (M–H) curves show that the FM observed is intrinsic for all the Ni-doped ZnO samples. However, the saturated magnetizations decrease gradually with increasing Ni concentration. This indicates that, in addition to FM, the excessive doping of Ni in ZnO also causes an antiferromagnetic (AFM) contribution which increases with increasing Ni amount. This result is also supported by the magnetization against temperature measurements. Furthermore, the trend of the ac-susceptibility (χ) versus temperature curves, measured under an ac-magnetic field of 100 Oe, also support our conclusion about the antiferromagnetic contribution to ferromagnetism in our samples.     

Synthesis,structural and optical characterization of Ni-doped ZnO nanoparticles

Nanocrystalline Zn_1−x Ni _x O (x = 0.00, 0.02, 0.04, 0.06, 0.08) powders were synthesized by a simple sol–gel autocombustion method using metal nitrates of zinc, nickel and glycine. Structural and optical properties of the Ni-doped ZnO samples annealed at 800 °C are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis using X-rays (EDAX), UV–visible spectroscopy and photoluminescence (PL). X-ray diffraction analysis reveals that the Ni-doped ZnO crystallizes in a hexagonal wurtzite structure and secondary phase (NiO) was observed with the sensitivity of XRD measurement with the increasing nickel concentration (x ≥ 0.04). The lattice constants of Ni-doped ZnO nanoparticles increase slightly when Ni²⁺ is doped into ZnO lattice. The optical absorption band edge of the nickel doped samples was observed above 387 nm (3.20 eV) along with well-defined absorbance peaks at around 439 (2.82 eV), 615(2.01 eV) and 655 nm (1.89 eV). PL measurements of Ni-doped samples illustrated the strong UV emission band at ~3.02 eV, weak blue emission bands at 2.82 and 2.75 eV, and a strong green emission band at 2.26 eV. The observed red shift in the band gap from UV–visible analysis and near band edge UV emission with Ni doping may be considered to be related to the incorporation of Ni ions into the Zn site of the ZnO lattice.     

Ferromagnetism in Cu-doped ZnO nanoparticles at room temperature

Cu-doped ZnO nanoparticles were successfully synthesized and structurally characterized by using X-ray diffraction (XRD) and transmission electron microscope (TEM). XRD shows that Zn_1−xCu_xO (x ≤ 0.04) samples are single phase with the ZnO-like wurtzite structure, while the secondary phase Cu is observed in Zn_0.95Cu_0.05O sample. Magnetic measurements indicated that Zn_1−xCu_xO (x = 0.02, 0.03, 0.04) are ferromagnetic at room temperature and the magnetic moment per Cu atom decreased with increasing Cu concentration. XRD, TEM and X-ray photoelectron spectroscopy (XPS) analysis revealed that no ferromagnetic-related secondary phase was detected. The origin of the ferromagnetism in Zn_1−xCu_xO (x ≤ 0.04) was mainly due to Cu ions substituted into the ZnO lattice.     

Room Temperature Ferromagnetism in Ni Doped ZnO Powders

Zn_1−x Ni _x O (x=0.1%, 0.4%, 0.7%, 1.0%) powders were prepared using the sol-gel technique, and the structural, optical, and magnetic properties of the samples were investigated. X-ray diffraction measurements show that all samples have a wurtzite structure and that the c-axis lattice constant decreases as the Ni content increases. X-ray photoelectron spectroscopy studies reveal that the doped Ni ions are in divalent states in all samples. Optical absorption spectra show that the band energy of Zn_1−x Ni _x O powders decreases with increasing Ni concentration. Photoluminescence measurements of Zn_1−x Ni _x O show a broad peak at a wavelength centered at about 467 nm which indicates the presence of a fraction of defects in ZnO. The room temperature ferromagnetism observed in all samples is intrinsic in nature.     

Optical and electrical properties of Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O thin films by sol–gel method

Mg _x Zn_1−x O (0 ≤ x ≤ 0.35) thin films have been deposited by sol–gel technique and the composition related structural, electrical, and optical properties are investigated. All the films have hexagonal wurtzite structure and the separation of MgO phase occurs when x = 0.3 and 0.35. With the increase of Mg content, the densification of the films decrease and band gap values increase. The maximum band gap value reaches 3.56 eV when x = 0.15. After Mg doping the conductivities of the Mg _x Zn_1−x O films are reduced greatly and the electrical current–voltage (I–V) characteristics show nonlinearity for x > 0.15.     

Effect of Mg content on structure and properties of Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O:Al UV transparent conducting films

Mg _x Zn_1−x O:Al (0 ≤ x ≤ 0.6) UV transparent conducting films were deposited on quartz glass by radio frequency magnetron sputtering. Effect of Mg content on structure, optical and electrical properties of Mg _x Zn_1−x O:Al films was investigated. There is a single phase of basic wurtzite structure of ZnO in Mg _x Zn_1−x O:Al films at x ≤ 0.4, and of a basic structure of cubic structure of MgO at x ≥ 0.6. The band gap can be varied from 3.27 to 5.90 eV by controlling Mg contents. The resistivity of Mg _x Zn_1−x O:Al films increase with increasing Mg content x due to the decrease of Al-doping efficiency. The electrical conduction of Mg _x Zn_1−x O:Al films can be markedly improved by increasing the Al-doping level appropriately and annealing in argon atmosphere at over 500 °C. The maximum band gap of Mg _x Zn_1−x O:Al films with wurtzite structure was found to be 5.35 eV when Mg content x is 0.4, and the minimum resistivity of 5.4 × 10⁻⁴ Ω cm was obtained when the Al/(Zn + Mg + Al) is 0.03 and the annealing temperature is over 500 °C. The average transmittance of Mg _x Zn_1−x O:Al films was higher than 86% in the wavelength region from 300 (x ≥ 0.4) to 800 nm.     

Structure and photocatalytic activity of Ni-doped ZnO nanorods

The one-dimensional (1D) Zn_1−xNi_xO (x = 0, 0.02, 0.05, 0.10) nanorods have been synthesized by a simple hydrothermal method. New bands show at ∼130 cm⁻¹ in the Raman spectra of Ni-doped ZnO nanorods and their relative intensity depends on the doping concentration of nickel. The optical band gap of the ZnO nanorods have been tuned by Ni-doping, which is revealed by absorption spectra. The photocatalytic activity of Zn_1−xNi_xO was studied by comparing the degradation rate of rhodamine B (RB) under UV-light irradiation. It was found that Zn_0.95Ni_0.05O exhibited the highest photocatalytic degradation efficiency among the samples.     

Applicability of the polymeric precursor method to the synthesis of nanometric single- and multi-layers of Zn1?xMnxO (x?=?0–0.3)

Polymeric precursor method (Pechini) was employed to fabricate single- and multilayers of Zn_1−x Mn _x O (x = 0–0.3) on glass substrates. X-ray diffraction measurements revealed that crystal structure of Zn_1−x Mn _x O multilayers is the typical hexagonal würzite structure of pristine ZnO. A reduced peak intensity and widened full width half maximum (FWHM) value of prominent peaks suggested that the Mn²⁺ ions have substituted the Zn²⁺ ion without changing the würzite structure of pristine ZnO up to Mn concentrations x ≤ 0.2. A distinct redshift of the absorption edge was observed as the Mn concentration x was increased. Additionally, the absorption edge was less sharp due, probably, to s–d and p–d interactions, which give rise to band gap bowing. Nevertheless, amorphous states appearing in the band gap as a consequence of reduced crystallinity may also be responsible for the shrinking of the band gap in this material. Interestingly, the field dependence of the magnetization showed typical paramagnetic behavior for all the chosen Mn concentrations with no evidence of ferromagnetic ordering. Probably, the absence of ferromagnetism in the studied Zn_1−x Mn _x O films is strongly related to defects (say Mn impurities at the interface between nano-crystallites) in ZnO due to partial substitution of host Zn ions by Mn ions.     

Structural and magnetic property studies on low temperature chemically synthesised one-dimensional Zn1−xNixO nanorods

One-dimensional Zn_1?xNi_xO nanorods have been established through a facile surfactant/template free low temperature hydrothermal route, which involves the direct growth of the nanorod-like structures from an aqueous alkaline phase. The monophasic wurtzite structure of the Ni-doped ZnO nanocrystallites were initially studied using the X-ray diffractograms and their rod-like morphological appearance and homogeneity were analyzed through the aid of electron microscopes. Moreover, the substitution of Ni ions was found to contain the oxygen related vacancies and defect states in the nanostructures, through suppressing the E₂(high) and E₁(LO) modes in the Raman spectra. A similar trend was also observed in the subband gap emission, over the visible region of the emission spectra. The magnetic property studies on the Zn_1?xNi_xO semiconducting nanorods revealed the presence of paramagnetic characteristics at room temperature and antiferromagnetic interactions at 20 K.     

Room Temperature Magnetism in Co-doped ZnO Nanorods

Zn_1−x Co _x O (x=0, 0.02, 0.04, 0.06, 0.08, 0.10) nanorods have been synthesized by the hydrothermal method. XRD patterns show that all samples are wurtzite structure without impurity. The magnetization measurements show that the pure ZnO is diamagnetic, while paramagnetism dominates in Zn_1−x Co _x O nanorods. Paramagnetism increases linearly with an increasing Co concentration. The magnetic moment calculated from the magnetic susceptibility is around 4 μ _B/Co, which is close to the theoretical value of Co ions with L=1.07 and S=3/2 in all Zn_1−x Co _x O nanorods, indicating the Co atoms are mostly isolated. All the samples exhibit weak ferromagnetism. However, the saturation magnetization of the ferromagnetic contribution in Zn_1−x Co _x O almost keeps constant with increasing Co concentration. We conclude that the weak ferromagnetism in Zn_1−x Co _x O might be due to the high concentration of defects.     

Synthesis and Characterization of ZnO and Ni Doped ZnO

ZnO and Zn_1−x Ni _x O (x=1, 2 and 3 mol %) were prepared by the sol gel via ultrasonication method with the Ni concentrations of 1, 2, and 3 mol %. The samples were characterized by high resolution scanning electron microscopy, X-ray diffraction, TEM, and UV-DRS spectroscopy. The XRD spectrum reveals that all the samples are of hexagonal wurtzite structures. The crystallite size decreases with increasing Ni concentration. The Ni concentration is determined by the energy dispersive X-ray technique. From the UV spectra, upon Ni doping the characteristic peak is red shifted which is the indication of decrease in the band gap. Magnetization measurements reveal that Ni doped ZnO shows paramagnetism with enhanced Ni concentration.     

Post-growth annealing and wide bandgap modulation of BeZnO layers grown by RF co-sputtering of ZnO and Be targets

ZnO based oxide system Be _x Zn_1−x O alloy of various compositions has been successfully grown by the RF co-sputtering method. The crystallinity of the Be _x Zn_1−x O alloys has been remarkably improved after the post-annealing at 600 °C compared with the Be _x Zn_1−x O alloys post-annealed at other temperatures. The x value of the Be _x Zn_1−x O layers has been increased from 0.022 to 0.17 by adjusting the RF-power of the Be target. Also, the optical bandgap energy has been modulated from 3.2218 to 3.7978 eV, respectively. Based on our results, a bandgap bowing parameter of Be _x Zn_1−x O alloy has been extracted out to be 4.5 eV. These findings could be useful to fabricate the ZnO/Be _x Zn_1−x O quantum structures and bandgap modulation for deep ultraviolet-light-emitting diodes.     

Spectroscopic studies of TeO<Subscript>2</Subscript>–ZnO–Er<Subscript>2</Subscript>O<Subscript>3</Subscript> glass system

Series of glass based on the (80 − x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ≤ x ≤ 2.5 mol%) has successfully been made by melt quenching technique. The optical properties of glass have been investigated by means of IR and Raman spectroscopy. It is observed that as the Er₂O₃ content is being increased, the sharp IR absorption peaks are consistently shifted from 650 to 672 cm⁻¹ while the Raman shift intensity around 640–670 cm⁻¹ is decreases but increases around 720–740 cm⁻¹. It is found out that both phenomenons are related to the structural changes between the stretching vibration mode of TeO₄ tbp and TeO₃ tp, and bending vibration mode of Te–O bonds in the glass linkages.     

Band gap modified Al-doped Zn1?xMgxO and Zn1?yCdyO transparent conducting thin films

Al-doped Zn_1−x Mg _x O and Zn_1−y Cd _y O thin films were prepared on glass substrates by sol–gel method. The codoping thin films showed preferential c-axis orientation, and the lattice constant c evaluated from the shift of the position of (002) peak displayed an increasing evolution from x = 8 at.% to y = 8 at.%, indicating a roughly statistical substitution of Mg²⁺ and Cd²⁺ for Zn²⁺ in their solid solution. The effects of narrowing and widening band gap (E _g) on conductivity of (Cd, Al) and (Mg, Al) codoped ZnO thin films were simultaneously investigated using transmission spectra and electrical measurements. The transmittances of these films are obviously decreased by vacuum annealing to 50–60%. However, the carrier concentration and Hall mobility both increase, and resistivity decreases with narrowing band gap in 1 at.% Al-doped Zn_1−x Mg _x O and Zn_1−y Cd _y O thin films from x = 8 at.% to y = 8 at.%. It is revealed that the conductivity of Al-doped ZnO thin films could be enhanced by this simple band gap modification.     

Effect of Ni Doping on Structural,Morphological, Optical and Magnetic Properties of Zn1−x Ni x O Dilute Magnetic Semiconductors

Ni²⁺-doped ZnO diluted magnetic semiconducting materials (Zn_1?x Ni _x O with x=0.01,0.02,0.03,0.04,0.05) were synthesised by the co-precipitation method. All synthesised samples were sintered at 600 °C for 6 hours. The effects of Ni²⁺ ion-doping on the structural, morphological, optical and magnetic properties of ZnO were investigated using powder X-ray diffraction, field emission SEM, UV–DRS spectroscopy, photoluminescence and vibrating sample magnetometry. The XRD patterns of pure and Ni-doped ZnO samples revealed single phase hexagonal wurtzite structure. The SEM analysis revealed the morphology of prepared samples, and the chemical compositions of all samples were analysed using exhibit energy density X-ray analysis (EDAX) characterisation. The absorption and emission properties revealed the effect of Ni²⁺ doping in ZnO samples. All Ni²⁺ ion-doped samples showed ferromagnetism at room temperature. The observed results are here analysed and reported.     

Thermodynamic principles of the synthesis of CdTe,ZnTe, and CdZnTe solid solutions

Results of thermodynamic investigations of the P-T-X phase equilibria in Cd-Te, Zn-Te and Cd-Zn-Te systems carried out by measuring total vapor pressure in the 1–760 Torr (0.13–101 kPa) range at temperatures up to ∼1370 K are systematized. Concentration boundaries of the existence of intermediate phases with the compositions CdTe_1±δ, ZnTe_1±δ, and Cd_{1 − x} Zn _x Te_1±δ (x = 0.05, 0.10, 0.15) are established. Vapor compositions in crystal-vapor equilibria are determined and isopleths of partial pressures for the CdTe_1±δ and Cd_{1 − x} ZnxTe_1±δ (x = 0.05, 0.10, 0.15) systems are calculated. Being presented in an analytical form, the thermodynamic data provide a basis for targeted synthesis of the indicated compounds.     

Investigation on the synthesis of (Zn<Subscript>1−x</Subscript>Mg<Subscript>x</Subscript>)TiO<Subscript>3</Subscript> and the modulation effect of CaTiO<Subscript>3</Subscript>

(Zn_1−xMg_x)TiO₃ (x = 0.1–0.5) solid solutions were synthesized by solid-state reaction using ZnO, (MgCO₃)₄·Mg(OH)₂·5H₂O and TiO₂ as raw materials. The influences of Zn: Mg ratio and calcining temperature on the properties of (Zn_1−xMg_x)TiO₃ were studied. By adding CaTiO₃ into (Zn_1−xMg_x)TiO₃, the microwave properties and sintering behavior were improved. The ceramics could be sintered at 1150 °C, and the ceramics with excellent microwave properties of τ_f ≈ ±10 ppm/°C, ε ≈ 24, Q × f > 45000 GHz (8 GHz) were obtained.     

Magnetoelectric and electrical properties of WO3-doped (Ni0.8Zn0.1Cu0.1)Fe2O4/[Pb(Ni1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–PbTiO3] composites

A total of 5 mol% WO₃-doped (1−x)(Ni_0.8Zn_0.1Cu_0.1)Fe₂O₄/xPb(Ni_1/3Nb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃ ((1−x)NZCF/xPNN-PZN-PT) magnetoelectric particulate ceramic composites were prepared by conventional solid-state reaction method via low-temperature sintering process. X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM) observation indicate that piezoelectric phase and ferrite phase coexist in the sintered particulate ceramic composites. Dielectric property of the (1−x)NZCF/x0.53PNN–0.02PZN–0.05Pb(Ni_1/2W_1/2)O₃–0.40PT ((1−x)NZCF/xPNN-PZN-PNW-PT, nominal composition) composites is improved greatly as compared to that of the undoped (1−x)NZCF/xPNN-PZN-PT composites. The WO₃-doped (1−x)NZCF/xPNN-PZN-PT composites exhibit typical P–E hysteresis loops at room temperature accompanied by the decrease of saturation polarization (P _s) and remnant polarization (P _r). At the same time, piezoelectric property of the composites deteriorates greatly with the increase of ferrite content. The (1−x)NZCF/xPNN-PZN-PNW-PT composites can be electrically and magnetically poled and exhibit apparent magnetoelectric (ME) effect. A maximum ME voltage coefficient of 13.1 mV/(cm Oe) is obtained in the 0.1NZCF/0.9PNN-PZN-PNW-PT composite at 400 Oe d.c. magnetic bias field superimposed 1 kHz a.c. magnetic field with 5 Oe amplitude. The addition of WO₃ in the piezoelectric phase decreases sintering temperature greatly from 1180 °C to 950 °C and decreases dielectric loss sharply of the composites, thus the ME voltage coefficient increases. Such ceramic processing is valuable for the preparation of magnetoelectric particulate ceramic composites with excellent ME effect.     

LO phonon–plasmon coupled modes and carrier mobilities in heavily Se-doped Ga(As, N) thin films

We use Raman scattering to study the LO–plasmon coupled modes (LOPCMs) of n-type GaAs_1−x N _x epilayers grown by molecular beam epitaxy (0.1% ≤ x ≤ 0.36%). We find that the LOPCMs are heavily damped in n-GaAs_1−x N _x even for x as low as 0.1%. From a lineshape analysis based on the hydrodynamical model, we evaluate the lifetime of the LOPCMs in our samples. We compare the values thus obtained with the corresponding Hall mobilities. We find that both quantities decrease strongly with increasing x, which can be attributed to N-related alloy scattering of conduction band electrons in the GaAs_1−x N _x alloy.     

Glasses formation,characterization, and crystal-structure determination in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–TeO<Subscript>2</Subscript> system prepared in an air

A glass-forming domain is found and studied within Bi₂O₃–Sb₂O₃–TeO₂ system. The glasses composition were obtained in pseudo-binary xSbO_1.5, (1−x)TeO₂ for 0.05 ≤ x ≤ 0.20. The constitution of glasses in the system Sb₂O₃–TeO₂ was investigated by DSC, Raman, and Infrared spectroscopy. The influence of a gradual addition of the modifier oxides on the coordination geometry of tellurium atoms has been elucidated based Infrared and Raman studies and showed the transition of TeO₄, TeO₃₊₁, and TeO₃ units with increasing Sb₂O₃ content. XRD results reveal the presence of three crystalline: γ-TeO₂, α-TeO₂, and SbTe₃O₈ phases during the crystallization process. The density of glasses has been measured. The investigation in the ternary system by the solid state reaction using XRD reveals the existence of a solid solution Bi_1−x Sb_1−x Te_2x O₄ isotopic to BiSbO₄ with 0 ≤ x ≤ 0.1.