Structural and magnetic properties of Co1−xZnxFe2O4 nanorods prepared by the solvothermal annealing method

Co_1−xZn_xFe₂O₄ (0.1≤x≤0.9) nanorods have been prepared by the thermal decomposition of the corresponding oxalate precursor, which was synthesized by the template-, surfactant-free solvothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM). The obtained Co_1−xZn_xFe₂O₄ (0.1≤x≤0.9) nanorods were built by many nanoparticles with average sizes around 20 nm to form one-dimensional arrays. Vibrating sample magnetometry measurements show that the coercivity of the ferrite nanorods decreases with increasing Zn content, whereas the specific saturation magnetization initially increases and then decreases with the increase of Zn content. The maximum saturation magnetization value of the as-prepared sample (Co_0.5Zn_0.5Fe₂O₄) reaches 43.0 emu g⁻¹.     

Ni0.5Zn0.5Fe2O4 nanoparticles and their magnetic properties and adsorption of bovine serum albumin

Ni_0.5Zn_0.5Fe₂O₄ nanoparticles were synthesized by the facile citrate-gel process and the preliminary measurement for adsorption of bovine serum albumin (BSA) protein on these nanoparticles was carried out. The gel precursor and resultant nanoparticles were characterized by TG-DSC, FTIR, XRD, TEM and VSM techniques and the BSA adsorption on the nanoparticles was analyzed by UV spectrophotometer at room temperature. The results show that the single phase of spinel Ni_0.5Zn_0.5Fe₂O₄ is formed at 400 °C. With increasing calcination temperature from 400 to 700 °C, the average grain size increases from about 14 to 45 nm and consequently, the specific saturation magnetization of Ni_0.5Zn_0.5Fe₂O₄ nanoparticles increases from about 46 to 68 Am²/kg. The coercivity initially increases and then decreases with increasing calcination temperature, with a maximum value 9.2 kA/m at 500 °C. The as-prepared Ni_0.5Zn_0.5Fe₂O₄ nanoparticles exhibit a good adsorbing ability for BSA and the optimized adsorption is achieved for the Ni_0.5Zn_0.5Fe₂O₄ nanoparticles calcined at 500 °C with grain size about 24 nm.     

Microstructure and dielectric properties of Ba0.6Sr0.4TiO3-MgAl2O4 composite ceramics

(1 − x)Ba_0.6Sr_0.4TiO₃-xMgAl₂O₄(x = 25, 30, 35 and 40 wt%) composite ceramics were prepared by conventional solid-state reaction method. The microstructures, dielectric properties and tunability of the composites have been investigated. The XRD patterns analysis reveals two crystalline phases, a cubic perovskite structure Ba_0.6Sr_0.4TiO₃ (BST) and a spinel structure MgAl₂O₄ (MA). SEM observations show that the BST grains slightly dwindle and agglomerate with increasing amounts of MA. A dielectric peak with very strong frequency dispersion is observed at higher MA content, and the Curie temperature shifts to a higher temperature with increasing MA content. The ceramic sample with 30 wt% MA has the optimized properties: the dielectric constant is 1503, the dielectric loss is 0.003 at 10 kHz and 25 °C, the tunability is 23.63% under a dc electric field of 1.0 kV/mm, which is suitable for ferroelectric phase shifter.     

Synthesis and magnetic properties of nanoporous Co3O4 nanoflowers

Nanoporous Co₃O₄ hierarchical nanoflowers have been prepared through sequential process of a hydrothermal reaction and heat treatment. These nanoflowers consisting of a great deal of Co₃O₄ nanofibers have bimodal pore structures and Brunauer–Emmett–Teller surface area of 34.61 m²/g. The temperature dependence curves of magnetization in zero-field-cooled and field-cooled exhibit main antiferromagnet and weak ferromagnet of Co₃O₄ nanoflowers at blocking temperature of 34 K, respectively. In addition, analysis of their optic properties obviously indicates red shift of absorption peaks, exhibiting quantum-confined effect and traits of semiconductor.     

Co3O4/CeO2 composite oxides for methane emissions abatement: Relationship between Co3O4–CeO2 interaction and catalytic activity

Co₃O₄/CeO₂ composite oxides with different cobalt loading (5, 15, 30, 50, 70 wt.% as Co₃O₄) were prepared by co-precipitation method and investigated for the oxidation of methane under stoichiometric conditions. Pure oxides, Co₃O₄ and CeO₂ were used as reference. Characterization studies by X-ray diffraction (XRD), BET, temperature programmed reduction/oxidation (TPR/TPO) and X-ray photoelectron spectroscopy (XPS) were carried out.

An improvement of the catalytic activity and thermal stability of the composite oxides was observed with respect to pure Co₃O₄ in correspondence of Co₃O₄–CeO₂ containing 30% by weight of Co₃O₄. The combined effect of cobalt oxide and ceria, at this composition, strongly influences the morphological and redox properties of the composite oxides, by dispersing the Co₃O₄ phase and promoting the efficiency of the Co³⁺–Co²⁺ redox couple. The presence in the sample Co₃O₄(30 wt.%)–CeO₂ of a high relative amount of Ce³⁺/(Ce⁴⁺ + Ce³⁺) as detected by XPS confirms the enhanced oxygen mobility.

The catalysts stability under reaction conditions was investigated by XRD and XPS analysis of the used samples, paying particular attention to the Co₃O₄ phase decomposition. Methane oxidation tests were performed over fresh (as prepared) and thermal aged samples (after ageing at 750 °C for 7 h, in furnace). The resistance to water vapour poisoning was evaluated for pure Co₃O₄ and Co₃O₄(30 wt.%)–CeO₂, performing the tests in the presence of 5 vol.% H₂O. A methane oxidation test upon hydrothermal ageing (flowing at 600 °C for 16 h a mixture 5 vol.% H₂O + 5 vol.%O₂ in He) of the Co₃O₄(30 wt.%)–CeO₂ sample was also performed. All the results confirm the superiority of this composite oxide.     

Physical,structural, morphological,magnetic and electrical properties of Co0.5-xNixZn0.5Fe2O4 nanocrystalline ferrites

A series of Co_0.5-xNi_xZn_0.5Fe₂O₄ (x?=?0–0.25 insteps of 0.05) nano crystalline ferrites were synthesized in combustion method using citric acid as fuel. Densities and porosities were calculated using the lattice constant and Archimedes's principle. A linear increase in experimental density and a decrease in porosity were observed with increase in nickel concentration. Cationic distribution was proposed on the basis of theoretical lattice constant and it was correlated with the variation in magnetic and electrical properties of all samples. TEM image of the sample with nickel concentration x?=?0.15 indicated the existence of nano-metric range particles and the sample was characterized with the help of inter-planar spacing(s) from SAED pattern. Morphological and surface analysis was studies using Scanning Electron Microscopy and well developed nearly spherical grains were observed with increase in nickel concentration. Energy Dispersive Spectroscopic (EDS) analysis was performed for all nickel substituted samples and all displayed stoichiometric proportions of ions in the samples as per the chemical composition. Elemental mapping was done for all samples using EDS data. Curie temperature was dropped nearly 90?°C at the end of the series. Initial permeability showed slight variation with an increase in nickel concentration and it remained nearly constant with frequency up to 3?MHz. Magnetic loss was observed to be constant for all samples after 100?kHz. DC Electrical resistivities of all samples were measured and all samples displayed resistivity in the order of 10⁸ Ω-cm. AC resistivity and dielectric studies were conducted from 100?Hz to 5?MHz for all samples. Dielectric constant and losses of all samples exhibited very low values compared to that of conventional ferrites. The electrical properties of all samples were discussed with the help of temperature variation of resistivity, activation energy, grain size, density and porosity.     

Characterization and low-temperature sintering of Ni0.5Zn0.5Fe2O4 nano-powders prepared by refluxing method

The as-prepared Ni_0.5Zn_0.5Fe₂O₄ powders fabricated directly from the solution of metal nitrates by the refluxing method were testified by the analysis of XRD, TEM, SAED and HRTEM. XRD pattern indicated that obtained Ni_0.5Zn_0.5Fe₂O₄ powders were single phase with spinel structure, TEM analysis showed that the powders with cubic shape were uniform in particle size of about 10-20 nm. Ceramics prepared by the as-synthesized Ni_0.5Zn_0.5Fe₂O₄ powders sintered at various temperatures between 950 °C and 1150 °C for 2 h were observed by SEM technique, which indicated that the Ni_0.5Zn_0.5Fe₂O₄ ferrites can almost be sintered to theoretic density at 1100 °C for 2 h, lower by at least about 200 °C compared with those ferrites prepared by the conventional oxide method. The relative magnetic loss tanδ/μ_i of the ceramic samples sintered at the temperature 1050 °C was measured to be of the order of 10^− 4-10^− 5 in the frequency range from 1 MHz to 10 MHz, and the threshold frequency of the ferrites was 77.2 MHz.     

Co2O3 substitution effects on the structure and microwave dielectric properties of low-firing (Zn0.9Mg0.1)TiO3 ceramics

Low-firing (Zn_0.9Mg_0.1)_1?xCo_xTiO₃ (x = 0.02–0.10) (ZMC_xT) microwave dielectric ceramics with high temperature stability were synthesized via conventional solid-state reaction. The influences of Co₂O₃ substitution on the phase composition, microstructure and microwave dielectric properties of ZMC_xT ceramics were discussed. Rietveld refinement results show the coexistence of ZnTiO₃ and ZnB₂O₄ phases at x = 0.02–0.10. (Zn_0.9Mg_0.1)_1?xCo_xTiO₃ ceramic with x = 0.06 (ZMC_0.06T) obtains the best combination microwave dielectric properties of: ε_r = 21.58, Q × f = 53,948 GHz, τ_f = ? 54.38 ppm/°C. For expanding its application in LTCC field, 3 wt% ZnO-B₂O₃-SiO₂ (ZBS) and 9 wt% TiO₂ was added into ZMC_0.06T ceramic, great microwave dielectric properties were achieved at 900 °C for 4 h: ε_r = 26.03, Q × f = 34,830 GHz, τ_f = ? 4 ppm/°C, making the composite ceramic a promising candidate for LTCC industry.     

Synthesis and magnetic properties of CoAlFe2O4 nanoparticles

Nanosized particles of CoAl_xFe_2-xO₄, where 0?≤?x?≤?2, were synthesized by the sol–gel combustion method and the magnetic properties of these compounds were investigated. According to X-ray diffractograms, the samples are single phase and the crystallite size is between 7 and 25?nm. The room temperature saturation magnetization of the samples was estimated from the cation distribution and ferromagnetic resonance spectra were used to determine the magnetocrystalline anisotropy. The results show that the saturation magnetization and the magnetocrystalline anisotropy vary over a wide range, from maxima of M_s =?0.42?MA/m and K?=?0.39?kJ/m³ for x?=?1.0 to minima of almost zero for x?≈?1.4, a result that could be useful for practical applications of these materials.     

Dielectric,magnetic and magnetoelectric properties of Ni0.5Zn0.5Fe2O4+Pb(Zr0.48Ti0.52)O3 composite ceramics

Magnetoelectric composite ceramics of spinel ferrite Ni_0.5Zn_0.5Fe₂O₄ (NZFO) with high magnetic permeability and tetragonal perovskite Pb(Zr_0.48Ti_0.52)O₃ (PZT) with high piezoelectric constant were synthesized by common solid state reaction method. XRD and SEM showed that high dense composite ceramics without any foreign phases were obtained. The ceramics showed excellent dielectric and magnetic properties, which were stable in a large frequency range. The dielectric peak became wider with the ferrite content in the permittivity spectrum with temperature. With the increase in the ferrite content, the magnetic Curie temperature shifted to higher temperature and closed to that of the pure ferrite. In addition, the magnetoelectric coefficient enhanced as the increase in the ferrite content. The properties of the composite ceramics could be adjusted by the ferrite content. These research results provided a powerful experimental basis for the sensor and transducer in microelectronic and microwave devices.     

Low temperature sintering of magnetic Ni0.5Co0.5Fe2O4 ceramics prepared from mechanochemically synthesized nanopowders

The effect of mechanochemichally synthesized nanoceramics Ni_0.5Co_0.5Fe₂O₄ (NCF) on the sintering process was studied. After 60?h of mechanochemichal treatment, the amount of formed ferrite phase reaches to about 70?vol%. From 60–100?h 10% increase in volume fraction of synthesized magnetic phase can be observed. Further increment in process time had no remarkable effect on the NCF phase formation. After 60?h, ceramic nanoparticle formation is directly reflected by TEM image and specific surface area (28?m²/g equivalent to 40?nm in diameter). The coercivity (Hc) shows a drastic diminution from 1996 to about 159?Oe by 60?h process time. Further milling treatment has no observable effect on the values of Hc. Additionally, the magnetization saturation (Ms) increases up to ~13?emu/g by 60?h mechanical milling of powders mixture. Thereafter from 60?h to 100?h, the Ms rapidly increased from 13 to 32?Oe. Finally, with continuing mechanochemichal process up to 130?h the Ms slightly diminished (~29?emu/g). Additionally, compared to synthesized powders the higher values of M_S (65?emu/g) and lower values of H_C (140?Oe) for sintered ceramic were detected. The low sintering temperature (1300?°C) for magnetic NCF sample prepared from nanoparticles may be caused by the high activity of nanoceramics.     

Structural,magnetic and magnetostrictive properties of Co1-xLixFe2O4 synthesized by cathode materials of spent Li-ion batteries

In this study, we investigated the effects of substituting Li⁺ for Co²⁺ at the B sites of the spinel lattice on the structural, magnetic and magnetostrictive properties of cobalt ferrites. The Li⁺ substituted cobalt ferrites, Co_1-xLi_xFe₂O₄, with x varying from 0 to 0.7 in 0.1 increments, were synthesized with a sol-gel auto-combustion method using the cathode materials of spent Li-ion batteries. X-ray diffraction analysis revealed that all the Co_1-xLi_xFe₂O₄ nanopowders had a single-phase spinel structure and the lattice parameters decreased with increasing Li⁺ content, which can be proved by slight shifts towards higher diffraction angle values of the (311) peak. Field emission scanning electron microscopy was used to observe the fractured inner surface of the sintered cylindrical rods and the increased porosity resulted in a decreased magnetostriction. The oxidation states of Co and Fe in the cobalt ferrite samples were examined by X-ray photoelectron spectroscopy. High resolution transmission electron microscopy micrographs showed that most particles were roughly spherical and with sizes of 25–35?nm. Li⁺ substitution had a strong effect on the saturation magnetization and coercivity, which were characterized with a vibrating sample magnetometer. The Curie temperature was reduced due to the decrease in magnetic cations and the weakening of the exchange interactions. The magnetostrictive properties were influenced by the incorporation of Li⁺ at the B sites of the spinel structure and correlated with the changes in porosity, magnetocrystalline anisotropy and the cation distribution.     

Catalytic performance of Co3O4/CeO2 and Co3O4/CeO2–ZrO2 composite oxides for methane combustion: Influence of catalyst pretreatment temperature and oxygen concentration in the reaction mixture

The influence of catalyst pre-treatment temperature (650 and 750 °C) and oxygen concentration (λ = 8 and 1) on the light-off temperature of methane combustion has been investigated over two composite oxides, Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ containing 30 wt.% of Co₃O₄. The catalytic materials prepared by the co-precipitation method were calcined at 650 °C for 5 h (fresh samples); a portion of them was further treated at 750 °C for 7 h, in a furnace in static air (aged samples).

Tests of methane combustion were carried out on fresh and aged catalysts at two different WHSV values (12 000 and 60 000 mL g⁻¹ h⁻¹). The catalytic performance of Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ were compared with those of two pure Co₃O₄ oxides, a sample obtained by the precipitation method and a commercial reference. Characterization studies by X-ray diffraction (XRD), BET and temperature-programmed reduction (TPR) show that the catalytic activity is related to the dispersion of crystalline phases, Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ as well as to their reducibility. Particular attention was paid to the thermal stability of the Co₃O₄ phase in the temperature range of 750–800 °C, in both static (in a furnace) and dynamic conditions (continuous flow). The results indicate that the thermal stability of the phase Co₃O₄ heated up to 800 °C depends on the size of the cobalt oxide crystallites (fresh or aged samples) and on the oxygen content (excess λ = 8, stoichiometric λ = 1) in the reaction mixture. A stabilizing effect due to the presence of ceria or ceria–zirconia against Co₃O₄ decomposition into CoO was observed.

Moreover, the role of ceria and ceria–zirconia is to maintain a good combustion activity of the cobalt composite oxides by dispersing the active phase Co₃O₄ and by promoting the reduction at low temperature.     

Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst

A series of CeO₂ promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N₂O). Addition of CeO₂ to Co₃O₄ led to an improvement in the catalytic activity for N₂O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N₂O conversion could be attained over the CoCe0.05 catalyst below 400 °C even in the presence of O₂, H₂O or NO. Methods of XRD, FE-SEM, BET, XPS, H₂-TPR and O₂-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO₂ could increase the surface area of Co₃O₄, and then improve the reduction of Co³⁺ to Co²⁺ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N₂O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO₂, are responsible for the enhancement of catalytic activity of Co₃O₄.     

Synergistic effect in structural and supercapacitor performance of well dispersed CoFe2O4/Co3O4 nano-hetrostructures

Herein, we report a facile homogeneous urea – assisted hydrothermal approach for the design of CoFe₂O₄/Co₃O₄ nano hetrostructure. A variation in Co concentration leads to smartly designed composite material namely CFC-11 and CFC-12 where CFC-12 appreciates the benefits of both CoFe₂O₄ and Co₃O₄ nanoparticles. The physico – chemical properties of as developed materials were investigated by X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron microscopy (XPS) and Raman spectroscopy. The specific surface area and pore size distribution was determined by Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halendo (BJH) respectively. Magnetic measurements via. vibrating sample magnetometer (VSM) demonstrate that saturation magnetization decreases with the incorporation of Co₃O₄ antiferromagnetic nanoparticles. To explore the utility of as designed nano-hetrostructures as supercapacitor electrodes, we employed cyclic voltammetry (CV) and electrochemical impedence spectroscopy (EIS) measurements. A high specific capacitance of 761.1?F?g^?1 at 10?mV?s^?1, admirable cyclic durability of 92.2% and a low resistance value obtained from impedence measurements was observed for CFC-12. The favorable performance demonstrates the synergistic effect of CoFe₂O₄ and Co₃O₄ nanoparticles and thus promise an excellent material for energy storage devices.     

Effect of CeO2 on the thermoelectric properties of WO3-based ceramics

The thermoelectric properties of tungsten trioxide (WO₃) ceramics doped with cerium dioxide (CeO₂) were investigated. The results demonstrated that the addition of CeO₂ to WO₃ could promote the grain growth and the densification. The magnitude of the electrical conductivity (σ) and the absolute value of the Seebeck coefficient (|s|) depended strongly on the CeO₂ content. The sample doped with 2.0 mol% CeO₂ yielded higher σ and |s|, resulting in a significant increase in the power factor (σs²). In addition, the power factor value of all samples increased abruptly at high temperatures, which revealed that WO₃-based ceramics could have greater thermoelectric properties at high temperatures.     

Phase composition,Raman spectra,infrared spectra and dielectric properties of Li2MgTi1-x(Mg1/3Nb2/3)xO4 ceramics at microwave frequency

The Li₂MgTi_1-x(Mg_1/3Nb_2/3)_xO₄ (0?≤x?≤?0.5) ceramics were prepared by the conventional solid-state method. The relationship among phase composition, substitution amount and microwave dielectric properties of the ceramics was symmetrically investigated. All the samples possess the rock salt structure with the space group of Fm-3m. As the x value increases from 0 to 0.5, the dielectric constant linearly decreases from 16.75 to 15.56, which can be explained by the variation of Raman spectra and infrared spectra. The Q·f value shows an upward tendency in the range of 0?≤x?≤?0.3, but it then decreases when x?>?0.3. In addition, the temperature coefficient of resonant frequency (τ_f) is shifted toward zero with the increasing (Mg_1/3Nb_2/3)⁴⁺ addition. By comparison, the Li₂MgTi_0.7(Mg_1/3Nb_2/3)_0.3O₄ ceramics sintered at 1400?°C can achieve an excellent combination of microwave dielectric properties: ε_r=?16.19, Q·f =?160,000?GHz and τ_f =??3.14?ppm/°C.     

Synthesis and magnetic properties of monodisperse CoFe2O4 nanoparticles coated by SiO2

The monodisperse CoFe₂O₄ nanoparticles were synthesized by a modified chemical coprecipitation method. Coating SiO₂ on the surface of the CoFe₂O₄ nanoparticles was carried out to keep single domain particles non-interacting with cubic magnetocrystalline anisotropy. The Curie temperatures (T_c) of the monodisperse CoFe₂O₄ nanoparticles can be accurately measured because the SiO₂ shells prevented the aggregation and growth of nanoparticles at high temperature. The magnetic properties of the CoFe₂O₄@SiO₂ nanoparticles with core-shell structure in a wide temperature range (300～950?K) were investigated. It is remarkable that the coercive field (H_c) of CoFe₂O₄ nanoparticles increased from about 760?Oe to 1806?Oe after being coated with SiO₂, which increased by 137.6% compared to the uncoated samples at 300?K. The saturation magnetization (M_s) of the CoFe₂O₄@SiO₂ nanoparticles is 34.59?emu/g, which is about 52% of the naked CoFe₂O₄ nanoparticles value (66.51?emu/g) at 300?K. The hysteresis loops of the CoFe₂O₄@SiO₂ nanoparticles showed an orderly magnetic behavior at high temperature, such as the M_s, remanence magnetization (M_r) and H_c decreased as temperature increasing, being equal to zero near T_c. This is a good indication that the CoFe₂O₄@SiO₂ nanoparticles are suitable for a wide variety of technological applications at high temperature.     

Fabrication and microwave absorbing properties of Li0.35Zn0.3Fe2.35O4 micro-belts/nickel-coated carbon fibers composites

The Li_0.35Zn_0.3Fe_2.35O₄ micro-belts were prepared by cotton template for the first time. The nickel-coated carbon fibers were obtained by the electroless plating method. The formation mechanism of the ferrite micro-belt was studied. The microwave absorption properties of the two layers absorbers containing Li_0.35Zn_0.3Fe_2.35O₄ micro-belts and nickel-coated carbon fibers composites were investigated in the frequency range of 30–6000 MHz. The absorbers of the Li_0.35Zn_0.3Fe_2.35O₄ micro-belts/nickel-coated carbon fibers composites have much better microwave absorption properties than the nickel-coated carbon fibers absorbers, and the microwave absorption properties of the composites are influenced by the content of the absorber.     

Steam reforming of ethanol over Co3O4/CeO2 catalysts prepared by different methods

In this paper, Co₃O₄/CeO₂ catalysts for steam reforming of ethanol (SRE) were prepared by co-precipitation and impregnation methods. The catalysts prepared by co-precipitation were very active and selective for SRE. Over 10%Co₃O₄/CeO₂ catalyst, ethanol conversion was close to 100% and hydrogen selectivity was about 70% at 450 °C. The catalysts were characterized by X-ray diffraction, temperature-programmed reduction (TPR) and BET surface area measurements. The preparation method influenced the interaction between cobalt and CeO₂ evidently. The incorporation of Co ions into CeO₂ crystal lattice resulted in weaker interaction between cobalt and ceria on catalyst surface. In comparison with catalysts prepared by impregnation, more cobalt ions entered into CeO₂ lattice, and resulted in weaker interaction between active phase and ceria on surface of Co₃O₄/CeO₂ prepared by co-precipitation. Thus, cobalt oxides was easier to be reduced to metal cobalt which was the key active component for SRE. Meanwhile, the incorporation of Co ions into CeO₂ crystal lattice was beneficial for resistance to carbon deposition.