Considering metal oxide nanoparticles as important technological materials, authors provide a comprehensive review of researches on metal oxide nanoparticles, their synthetic strategies, and techniques, nanoscale physicochemical properties, defining specific industrial applications in the various fields of applied nanotechnology. This work expansively reviews the recent developments of semiconducting metal oxide gas sensors for environmental gases including CO2, O2, O3, and NH3; highly toxic gases including CO, H2S, and NO2; combustible gases such as CH4, H2, and liquefied petroleum gas; and volatile organic compounds gases. The gas sensing properties of different metal oxides nanoparticles towards specific target gases have been individually discussed. Promising metal oxide nanoparticles for sensitive and selective detection of each gas have been identified. This review also categorizes metal oxides sensors by analyte gas and also summarizes the major techniques and synthesis strategies used in nanotechnology. Additionally, strategies, sensing mechanisms and related applications of semiconducting metal oxide materials are also discussed in detail. Related applications are innumerable trace to ultratrace-level gas sensors, batteries, magnetic storage media, various types of solar cells, metal oxide nanoparticles applications in catalysis, energy conversion, and antennas (including microstrip and patch-type optically transparent antennas), rectifiers, optoelectronic, and electronics.

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Metal oxide nanoparticles and their applications in nanotechnology

This review aims to summarise the progress in some materials and structures for electromagnetic applications, such as microwave absorption, electric shielding and antenna designs, which have been developed in recent years. Composites with spherical powders for microwave absorption focus mainly on those based on ferrites (especially hexagonal), carbonyl iron and related alloys and various newly emerged nanosized materials. Composites with long conductive fibres as fillers will be summarised, with speical attentions to prediction, measurment and evaluation of their performances. Metamaterials include structures for microwave absorbing applications, tunable materials or structures with reflection or transmission coefficients that are tunable by external magnetic or electric fields, and specially designed structures for microwave absorbing applications, with thickness much smaller than that of conventional composite materials and performances that can be optimised by the physical properties of substra...

Recent progress in some composite materials and structures for specific electromagnetic applications

The synthesis and functional characterization of dense bulk nanometric oxides are reviewed, with particular emphasis on the modifications that a grain size in the low nanometric range (10–50 nm) introduces in their physical properties. The preparation of ceramics with low porosity and extremely small grain size is particularly challenging and mostly relies on the sintering of extremely fine nanopowder. The most popular methods for the preparation of the starting nanopowders are introduced and briefly discussed as well as the most widely employed densification techniques. The role of nanostructure in controlling phase stability, electrical and thermal transport, optical and magnetic properties of nano-oxides is discussed in details. Several examples are given where bulk materials prepared with grain size equal or below 50 nm show characteristics that are either enhanced or, in some cases, completely different from those possessed by the same materials, but with larger grain sizes.

Densification and properties of bulk nanocrystalline functional ceramics with grain size below 50nm

Recent advances in synthesis, characterization, and applications of nanoparticles for contaminated water treatment- A review

A series of Gd3+ doped nanocrystalline Co-ferrites CoGdxFe2-xO4 (x = 0.0 to 0.1) has been prepared by sol-gel auto combustion technique. Structural and morphology studies were performed using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Indexed XRD patterns confirm the formation of pure cubic spinel phase. Average crystallite sizes ranges from 16 nm to 25 nm ±2, were calculated from Sherrer's formula and Williamson Hall plots. Crystal strain increases with increase in doping amount of trivalent Gd ion. Lattice constant (a) and crystallite size D (311) increases with increase in Gd3+ concentration due to large ionic radii (0.94nm) of Gd3+ replacing Fe3+ (0.64nm). SEM images show the spherical morphology and uniform size distribution. Room temperature DC electrical resistivity decreases (~106) for x=0.025 then increases up to x=0.1 ~ (4.5×107). Dielectric properties have been studied using RF Impedance/material analyzer in the frequency range of 1 MHz to 1GHz. All the studied samples show a semi-conducting behavior as Permittivity and tangent loss (tanδ) decreases with the substitution of Gd3+ in parent crystal structure and have values of 4.92 and 0.016 at 1 GHz respectively. Complex impedance and Complex electric modulus plots were further studied for complete contribution of grains and grain boundary resistances to conduction and resonance frequencies respectively. Magnetic studies by Vibrating Sample Magnetometer (VSM) shows that magnetization (Ms) decreases with increase in Gd3+ concentration from 63 emu/gm to 27.26 emu/gm. Coercivity (Hc) first decreases for x=0.025, after which it increases to 2308 Oe for x=0.1.

https://iopscience.iop.org/article/10.1088/1742-6596/439/1/012015/pdf

Influence of Rare Earth (Gd3+) on Structural, Gigahertz Dielectric and Magnetic Studies of Cobalt ferrite

Novel magnetodielectric nanomaterials with matching permeability and permittivity for the very-high-frequency applications

Smart magnetodielectric nano-materials for the very high frequency applications

Indium substituted nano nickel zinc ferrites Ni0.5Zn0.5InxFe2-xO4 with x=0, 0.1, 0.2 and 0.3 are synthesized by a coprecipitation method. Magnetic and dielectric properties are studied over a frequency range 1-30 MHz. Initial permeability is found to be in the range of 9-19 with a magnetic loss tangent of 10-1-10-2 . The dielectric constant is noticed in the range of 11-17 along with low dielectric loss tangent (10-1-10-3). The composition with x=0.2 is found to have the highest specific saturation magnetization of 78.8 emu/g. Appreciable dielectric and magnetic values along with low losses can be correlated to small grain size and better compositional stoichiometry obtained as a result of processing by coprecipitation method. These fascinating dielectric and magnetic properties of these materials reveal a direction for high-frequency applications.

Enhancement in Dielectric and Magnetic Properties of ${\rm In}^{3+}$ Substituted Ni-Zn Nano-Ferrites by Coprecipitation Method

The effective relative permittivity and effective relative permeability of magneto-dielectric materials when used as substrate for microstrip antenna shows interdependency. This dependency was analyzed through simulation and verified by synthesizing nano composite ferrite. The 40nm nano crystallite size particles were synthesized using a co- precipitation method. Matching values of complex permittivity (e* = 4.2-0.1j) and complex permeability (μ* = 4.3-0.2j) at 1 GHz were obtained from the electromagnetic characterization. The microstrip antenna with coaxial feed was fabricated and the interdependence of relative permittivity and relative permeability was verified. An error of 7% in the drawn length was observed for er and μr of the order of 4. The magneto-dielectric material with composition Mn0.5Zn0.3Co0.2Fe2O4+BaFe12O19 proposed in this paper definitely can be proposed as a substrate material for miniaturized antenna. The antenna with desired resonant frequency can be fabricated by calculating the effe...

Dielectric parameter estimation of novel magneto-dielectric substrate based microstrip antenna

Hexaplana W-type barium ferrite of nominal composition BaZn1.5Co0.5Fe16O27 was prepared by a co-precipitation method. The structural and electrical properties were studied at different sintering temperatures. The average crystallite size was found to be in the range 46 ‒ 57 nm calculated by Scherrer formula, which means crystallite size increases with an increase in sintering temperature. Fourier transform spectroscopy reveals the ferrite peaks in the range 577.19 cm−1 ‒ 595.48 cm−1 confirming the hexagonal structure of ferrites. Metal-Semiconductor transition temperature was found to be decrease as the sintering temperature increases, whereas the trend for activation energy was found to be increasing.

Preeti Thakur

Papers

Novel magnetodielectric nanomaterials with matching permeability and permittivity for the very-high-frequency applications

Smart magnetodielectric nano-materials for the very high frequency applications

Enhancement in Dielectric and Magnetic Properties of ${\rm In}^{3+}$ Substituted Ni-Zn Nano-Ferrites by Coprecipitation Method

Dielectric parameter estimation of novel magneto-dielectric substrate based microstrip antenna

Study of electrical properties of W-type barium hexaferrite for high frequency application