Zinc Oxide Nanoparticles for Varistors

Diwald, Oliver

doi:10.1002/9781119436782.ch23

Cited by 5 publications

(8 citation statements)

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“…Until now, most groups have focused on the materials’ ferroelectric response to explain the changes observed in charge separation and photocatalytic activities of BTO‐based photocatalysts. [ 6–8 ] However, the additional influence of point defects, found within most metal oxide nanoparticles, [ 9 ] on the BTO photochemical activity is still lacking. In particular, the creation of point defects under specific synthesis conditions that can act as charge recombination centers has been mostly ignored with these materials systems.…”

Section: Introductionmentioning

confidence: 99%

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Charge Separation in BaTiO₃ Nanocrystals: Spontaneous Polarization Versus Point Defect Chemistry

Neige

Schwab

Musso

et al. 2023

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However, the additional influence of point defects, found within most metal oxide nanoparticles, [9] on the BTO photochemical activity is still lacking. In particular, the creation of point defects under specific synthesis conditions that can act as charge recombination centers has been mostly ignored with these materials systems.Our work intends to fill this gap by studying the influence of ferroelectric effects and point defects on charge separation within various BTO nanoparticles. The photogenerated charge separation yield was quantified by combining O 2 photoadsorption experiments with electron paramagnetic resonance (EPR), using molecular oxygen as an electron scavenger. Compared to the reference TiO 2 anatase nanoparticles of similar size and surface area, BTO nanoparticles annealed at 600 °C have a charge separation yield that is > 10 times higher. This is attributed to the beneficial effect of the perovskite lattice on charge separation. Strikingly, we also report a counter-intuitive decrease in charge separation yield with increasing tetragonal BTO particle size, due to the formation of point defects during the annealing process that acts as recombination centers. [10] Results and DiscussionBaTiO 3 nanoparticles, synthesized via flame spray pyrolysis (FSP, details in the Experimental Section), were subjected to thermal treatment at temperatures ranging from 600 to 900 °C in alternating cycles of continuous pumping (p < 10 −5 mbar) and in an oxygen atmosphere (20 mbar) to remove residual carbon, surface hydroxyls and water (Figure S1, Supporting Information). The resulting nanoparticles are equiaxed, nonfaceted, and crystalline (Figure 1a,b). X-ray diffraction (XRD) patterns (Figure 1c) reveal a cubic crystal structure with broadened diffraction features that depend on the annealing temperature. Annealing at 700, 800, and 900 °C results in a reduction of the diffraction peak widths that indicates crystallite domain size growth.Annealing at 600 °C gives rise to BTO particles with an average crystallite domain size of ≈11 nm, consistent with the average particle size of 13 nm measured via TEM (Figure S1, Supporting Information). Annealing at higher temperatures The fate of photogenerated charges within ferroelectric metal oxides is key for photocatalytic applications. The authors study the contributions of i) tetragonal distortion, responsible for spontaneous polarization, and ii) point defects, on charge separation and recombination within BaTiO 3 (BTO) nanocrystals of cubic and tetragonal structure. Electron paramagnetic resonance (EPR) in combination with O 2 photoadsorption experiments show that BTO nanocrystals annealed at 600 °C have a charge separation yield enhanced by a factor > 10 compared to TiO 2 anatase nanocrystals of similar geometries. This demonstrates for the first time the beneficial effect of the BTO perovskite nanocrystal lattice on charge separation. Strikingly, charge separation is considerably hindered within BTO nanoparticles annealed ≥ 600 °C, due to the formation of Ba-O divacan...

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

Charge Separation in BaTiO₃ Nanocrystals: Spontaneous Polarization Versus Point Defect Chemistry

Neige

Schwab

Musso

et al. 2023

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“…The significant regions of the I–V curves of MOVs are as follows: (i) the prebreakdown or leakage region (I < 10 μA), (ii) the nonlinear region or normal varistor operation (10 μA < I < 1 kA), and (iii) the upturn region (I > 1 kA) [ 51 , 52 ]. At low currents, MOVs can reach very high resistance (≤10 GΩ) in the leakage region, which varies with temperature and frequency.…”

Section: Introductionmentioning

confidence: 99%

“…Normal varistor operation begins at a threshold or breakdown voltage (V B ) at a current of 1 mA, denoted as V 1mA , when α can reach a maximum value [ 52 , 53 , 55 ]. An α value greater than 30 suggests good contact between ZnO grains [ 53 ], while an α value less than 10 indicates poor boundary junctions between ZnO grains, resulting in unsatisfactory electrical (E–J) characteristics of MOVs [ 53 , 56 ].…”

Section: Introductionmentioning

confidence: 99%

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Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review

Lungu¹

2023

Materials

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This article reviews the progress in developing ZnO-V2O5-based metal oxide varistors (MOVs) using powder metallurgy (PM) techniques. The aim is to create new, advanced ceramic materials for MOVs with comparable or superior functional properties to ZnO-Bi2O3 varistors using fewer dopants. The survey emphasizes the importance of a homogeneous microstructure and desirable varistor properties, such as high nonlinearity (α), low leakage current density (JL), high energy absorption capability, reduced power loss, and stability for reliable MOVs. This study investigates the effect of V2O5 and MO additives on the microstructure, electrical and dielectric properties, and aging behavior of ZnO-based varistors. The findings show that MOVs with 0.25–2 mol.% V2O5 and MO additives sintered in air over 800 °C contain a primary phase of ZnO with a hexagonal wurtzite structure and several secondary phases that impact the MOV performance. The MO additives, such as Bi2O3, In2O3, Sb2O3, transition element oxides, and rare earth oxides, act as ZnO grain growth inhibitors and enhance the density, microstructure homogeneity, and nonlinearity. Refinement of the microstructure of MOVs and consolidation under appropriate PM conditions improve their electrical properties (JL ≤ 0.2 mA/cm2, α of 22–153) and stability. The review recommends further developing and investigating large-sized MOVs from the ZnO-V2O5 systems using these techniques.

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Effect of additive particle size on degradation behavior of ZnO varistors under high current surges

Gao,

Wang,

Yang

et al. 2024

J Mater Sci: Mater Electron

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Zinc Oxide Nanoparticles for Varistors

Cited by 5 publications

References 57 publications

Charge Separation in BaTiO₃ Nanocrystals: Spontaneous Polarization Versus Point Defect Chemistry

Charge Separation in BaTiO₃ Nanocrystals: Spontaneous Polarization Versus Point Defect Chemistry

Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review

Effect of additive particle size on degradation behavior of ZnO varistors under high current surges

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Zinc Oxide Nanoparticles for Varistors

Cited by 5 publications

References 57 publications

Charge Separation in BaTiO3 Nanocrystals: Spontaneous Polarization Versus Point Defect Chemistry

Charge Separation in BaTiO3 Nanocrystals: Spontaneous Polarization Versus Point Defect Chemistry

Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review

Effect of additive particle size on degradation behavior of ZnO varistors under high current surges

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Charge Separation in BaTiO₃ Nanocrystals: Spontaneous Polarization Versus Point Defect Chemistry

Charge Separation in BaTiO₃ Nanocrystals: Spontaneous Polarization Versus Point Defect Chemistry