Small Amount Of Monoclinic Phase Research Articles

Superelasticity and shape memory effect in zirconia nanoparticles

Superelasticity and shape memory effect are two key properties of zirconia-based ceramics which are mediated by the reversible tetragonal to monoclinic phase transformation. Although experimental studies discovered that the shape memory behavior of ceramics can be improved by reducing the grain boundary density, degradation in shape memory response still happens after a few cycles of loading–unloading–heating–cooling. In this work, superelastic and shape memory properties of single crystalline and polycrystalline yttria stabilized tetragonal zirconia (YSTZ) nanoparticles are studied by atomistic simulations. Fully recoverable superelastic strain (8.3%) is observed in a single crystalline nanoparticle by merely removing the compressive load. However, the shape memory behavior degrades with the increase of loading–unloading–heating–cooling cycles. In other words, a higher temperature is required for an additional strain recovery, but certain residual displacement may still remain after few cyclic loadings. Amorphous phase formation and its accumulation around the applied load contact area, as well as an increase in surface roughness are responsible for the observed degradation of shape memory response. In a polycrystalline YSTZ nanoparticle, besides the regular reverse transformation at the end of cyclic loading, most amorphous phase transfers back to the original tetragonal structure. However, a small amount of monoclinic phase is restrained by the permanent amorphous phase and grain boundaries at the end of cyclic loading, causing degradation of shape memory behavior.

Influence of temperature on structural-phase changes and physical properties of ceramics on the basis of aluminum oxide and silicon

Abstract The purpose of this experiment was to prepare high-voltage porcelain ceramics as local raw materials. Density, water absorption, and volume shrinkage were determined according to the State standard (GOST 7025-91). A structural analysis was carried out using a scanning electron microscope, and an X-ray phase analysis was carried out on an Xpert PRO diffractometer. It was found, that in the initial state, ceramics consist of hexagonal (SiO2) and a small amount of monoclinic phase. Above a temperature of 1150 °С they consist of hexagonal (SiO2), an orthorhombic lattice, and also contain mullite (Al2Si2O13).

Influence of temperature on structural-phase changes and physical properties of ceramics on the basis of aluminum oxide and silicon

Abstract The purpose of this experiment was to prepare high-voltage porcelain ceramics as local raw materials. Density, water absorption, and volume shrinkage were determined according to the State standard (GOST 7025-91). A structural analysis was carried out using a scanning electron microscope, and an X-ray phase analysis was carried out on an Xpert PRO diffractometer. It was found, that in the initial state, ceramics consist of hexagonal (SiO2) and a small amount of monoclinic phase. Above a temperature of 1150 °С they consist of hexagonal (SiO2), an orthorhombic lattice, and also contain mullite (Al2Si2O13).

Ferroelectricity in YO1.5-HfO2 films around 1 μm in thickness

Ferroelectricity has been demonstrated in polycrystalline 7%Y-doped HfO2 (YHO7) films with thicknesses ranging from 10 to 930 nm, which were grown on (111)Pt/TiOx/SiO2/(001)Si substrates by pulsed laser deposition at room temperature and subsequent annealing at 1000 °C. The X-ray diffraction pattern suggested that the major crystal phase consists of orthorhombic/tetragonal phases with a small amount of monoclinic phase even for the 930-nm-thick film despite its thickness. Moreover, the hysteresis loops associated with the ferroelectric orthorhombic phase were clearly observed for all samples including even the 930-nm-thick film. The remnant polarization (Pr) and the coercive field (Ec) are 14–17 μC/cm2 and 1300–1600 kV/cm, respectively, at max applied electric fields of ∼4000 kV/cm for all YHO7 films within the present study. These results indicate that the ferroelectric structure and properties of YHO7 films are insensitive to the film thickness.

Optical and ionic transport mechanism γ-phase stabilized nanostructured Bi-Ce-O ionic conductors: a structure-property correlation study

This work reports the body-centered cubic (BCC) γ-phase stabilization of Bi2O3 nanostructures by means of varying Ce doping concentration and its effect on the optical, ionic transport and dielectric properties. The Rietveld analysis of X-ray diffraction pattern confirmed the formation of nanocrystalline Ce-doped Bi2O3 composite nanostructure having BCC as main phase in addition with small amount of monoclinic phase at room temperature for 30% doping concentration in the pure Bi2O3 matrix. The results of TEM, EDAX and XRF analysis are consistent with the Rietveld analysis. Lattice fringe and SAED pattern obtained from HRTEM analysis confirm the body-centered cubic γ-phase as dominant phase. The UV-Vis spectroscopy study shows decrease in optical band gap with doping concentration. The presence of different molecular bonds corresponding to γ-phase has been confirmed using FT-IR spectroscopy. The ionic conductivity of the samples has been found to increase with measuring temperature as well as doping concentration. The dielectric and complex modulus properties have been analyzed using Havriliak-Negami formalism and found to be non-Debye type. The conductivity data has been found to obey Variable Range Hopping phenomenon which is corroborated with the structural property of the prepared compositions.

Effects of Cr Doping on Physical and Electrochemical Properties of Li2MnSiO4 Cathode Materials for Li-Ion Batteries

INTRODUCTION Lithium metal othosilicate (Li2 MSiO4, where M = Fe, Mn, Co or Ni) has currently attracted a good deal of interest as a high voltage positive electrode material due to its high theoretical charge and discharge capacities of 330 mAh g-1 and high voltage up to 5.1 V. Such high capacity arises from the ability to extract two lithium ions per one transition metal. However, this class of material has been reported to exhibit low conductivity and poor cycling performance due to structural instabilities with the transition from orthorhombic to monoclinic phase during charge and discharge.[1] Mn-site doping with transition metal ions (Ni2+, Cr2+, Ti4+, V5+) or the aliovalent ions (Al3+, Ga3+) can induce defects in the lattice and stabilize overall structure. Since the structural instability is generally caused by the collapse of MnO4 coordination structure to MnO6, works have been done to retain the MO4 structure.[2] A study by Cheng, et al. reported that substituting Cr on Mn site partly helps retain M-O coordination of MnO4.[3] In this study, our research focuses on stabilizing an othosilicate-based positive lithium-ion battery electrode material, specifically, lithium manganese silicate (Li2MnSiO4) via partial substitution of Mn with Cr up to 15 mol%. To understand the effect of Cr doping on structural evolution during the charge/discharge process, the in situ XRD is also conducted to understand the correlation between the electrode material’s structural and electrochemical behavior. EXPERIMENTAL Li2Mn1-x Cr x SiO4 (x = 0 - 0.15) were prepared by with an acetic acid-assisted sol–gel method. The dried materials were fired at 800°C for 6 hours in Ar atmosphere. Structural properties of the synthesized samples were studied by X-ray diffraction (Rigaku TTRAXII) using Cu-Kα (λ=1.5418 Å) radiation. Particle morphologies and size of the resulting compounds were observed using a field emission scanning electron microscope (FE-SEM, Hitachi SU8030). Electrochemical characterizations were performed by in Swagelok® cells. Active material, conductive carbon black and polyvinylidene fluoride (PVDF) were mixed in the ratio of 87:5:8 by weight. Galvanostatic charge-discharge cycling was done between 1.5-4.8 V at 0.05C using a MACCOR Series 4000 at room temperature. RESULTS AND DISCUSSIONS Figure 1 shows XRD patterns of the synthesized Li2Mn1-x Cr x SiO4 where Cr = 0 - 0.05. Main diffraction peaks could be indexed as an orthorhombic unit cell with a space group Pmnb. Appearance of the evidence of small amount of monoclinic phase, MnO and Li2SiO3. There is no obvious evidence of a phase containing Cr. With an increasing the Cr doping ratio, the unit cell volume slightly increases from 339.52 Å3 to 339.79 Å3 as expected due to larger ionic radii of Cr2+ than Mn2+ indicating the substitution of Cr into the structure of Li2MnSiO4. Electrochemical performance in relations to structural stability of Li2Mn1-x Cr x SiO4 will be discussed in the meeting. REFERENCES [1] R. Dominko, M. Bele, A. Kokalj, M. Gaberscek, J. Jamnik, Journal of Power Sources, 2007, 174, 457-461. [2] V.V. Politaev, A.A. Petrenko, V.B. Nalbandyan, B.S. Medvedev, E.S. Shvetsova, The Journal of Solid State Chemistry, 2007, 180, 1045–1050. [3] H.M. Cheng, S.X. Zhao, X. Wu, J.W. Zhao, L. Wei, Applied Surface Science, 2018, 433, 1067-1074. Fig. 1 Powder X-ray diffraction patterns of Li2Mn1-x Cr x SiO4 (x = 0, 0.025 and 0.05). Figure 1

Effect of different grinding burs on the physical properties of zirconia.

PURPOSEGrinding with less stress on 3Y-TZP through proper selection of methods and instruments can lead to a long-term success of prosthesis. The purpose of this study was to compare the phase transformation and physical properties after zirconia surface grinding with 3 different grinding burs.MATERIALS AND METHODSForty disc-shaped zirconia specimens were fabricated. Each Ten specimens were ground with AllCeramic SuperMax (NTI, Kahla, Germany), Dura-Green DIA (Shofu Inc., Kyoto, Japan), and Dura-Green (Shofu Inc., Kyoto, Japan). Ten specimens were not ground and used as a control group. After the specimen grinding, XRD analysis, surface roughness test, FE-SEM imaging, and biaxial flexural strength test were performed.RESULTSAfter surface grinding, small amount of monoclinic phase in all experimental groups was observed. The phase change was higher in specimens, which were ground with Dura-Green DIA and AllCeramic SuperMax burs. The roughness of surfaces increased in specimens, which were ground with Dura-Green DIA and AllCeramic SuperMax burs than control groups and ground with Dura-Green. All experimental groups showed lower flexural strength than control group, but there was no statistically significant difference between control group and ground with Dura-Green DIA and AllCeramic SuperMax burs. The specimens, which were ground with Dura- Green showed the lowest strength.CONCLUSIONThe use of dedicated zirconia-specific grinding burs such as Dura-Green DIA and AllCeramic SuperMax burs decreases the grinding time and did not significantly affect the flexural strength of zirconia, and therefore, they may be recommended. However, a fine polishing process should be accompanied to reduce the surface roughness after grinding.

Characterization of laser sealed coatings of yttria partially stabilized zirconia

Abstract The present paper reports an experimental investigation based on X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and wavelength dispersive spectroscopy (WDS) analyses of phases formed after laser sealing of plasma sprayed coatings of 8.5 wt% yttria partially stabilized zirconia (YPSZ). X-ray diffraction and X-ray step-scanning analyses showed that the plasma sprayed and sealed coatings consisted mainly of t ′ phase with a very small amount of monoclinic phase ( m phase) in the plasma sprayed coatings. It was also found that the small amounts of m and cubic phases ( c phase) present in the sealed coatings were dependent on laser processing specific energies (specific energy is equal to laser power/traverse speed x beam diameter). It was also found that rhombohedral ( r ) phase formed after laser sealing of coatings at higher specific energies. A direct relationship between c / a ratio of transformable tetragonal phase ( t phase) produced by thermal treatment of sealed coatings and nontransformable tetragonal phase ( t ′ phase) and the amount of Yttria was obtained. A new equation was derived, which describes the relationship between Yttria concentration and the c / a ratio of tetragonal phases ( t or t ′).

Effect of gadolinia on phase structure and thermal conductivity of ZrO 2–4.5 mol%Y 2O 3 ceramics

This paper deals with the effect of gadolinia on the phase structure and thermal conductivity of ZrO 2–4.5 mol%Y 2O 3 (YSZ) ceramics for thermal barrier coatings. The YSZ–Gd 2O 3 ceramics were synthesized by solid state reaction at 1500 °C for 2 h in air. The relative density, structure of different YSZ–Gd 2O 3 ceramics and thermal diffusivity in a temperature range of room temperature to 1200 °C were investigated by the Archimedes method, X-ray diffraction and laser-flash method. The ZrO 2–4.5 mol%Y 2O 3 (YSZ) ceramics consist of tetragonal, cubic and a small amount of monoclinic phase, and the YSZ–1.5 mol%Gd 2O 3 ceramics consist of both tetragonal and cubic phases. However, the YSZ–3.0 mol%Gd 2O 3, YSZ–4.5 mol%Gd 2O 3 and YSZ–6.0 mol%Gd 2O 3 ceramics only exhibit a cubic structure. The thermal conductivity of YSZ–Gd 2O 3 ceramics decreases with the increase of gadolinia content under identical temperature conditions. The thermal conductivities of the YSZ and YSZ–1.5 mol%Gd 2O 3 ceramics first decrease gradually with the increase of temperature below 800 °C and then increase slightly above 800 °C. The thermal conductivities of the YSZ–3.0 mol%Gd 2O 3, YSZ–4.5 mol%Gd 2O 3 and YSZ–6.0 mol%Gd 2O 3 ceramics are almost constants from room temperature to 1200 °C.

PAC characterization of Gd and Y doped nanostructured zirconia solid solutions

A perturbed angular correlation (PAC) study as a function of temperature has been carried out on spray pyrolysis-derived powders and compacts of 2.5 mol% Y 2O 3–ZrO 2 and 2 mol% Gd 2O 3–ZrO 2 nanostructured tetragonal zirconias. The powders undergo the ordinary thermal transformation between the two known defective t′- and regular t-tetragonal forms and also a partial and irreversible change to an ordered cubic configuration. The dynamical nature of the t′-form leads to an activation energy of about 0.15 eV for the oxygen vacancies movement. The as-obtained compacts do not exhibit any known cubic nanostructure but some additional contributions. In both of them a hyperfine component assigned to the orthorhombic phase is determined. In the smaller cation Y doped ceramic a small amount of monoclinic phase reflects an incomplete stabilization.

Transmission electron microscopy characterization of a Yttria-stabilized zirconia coating fabricated by electron beam–physical vapor deposition

Yttria-stabilized zirconia (YSZ) film was deposited on to a metal substrate by electron beam–physical vapor deposition (EB–PVD) at 850 °C. The film was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The YSZ film predominantly consisted of the tetragonal phase with a small amount of monoclinic phase. In addition, the film was composed of inverted triangular-based pyramidal grains (T-grains) and inverted diamond-based pyramidal grains (D-grains). The T-grains were aligned in the <111> direction and D-grains in <110>. Furthermore, striated lines of nanopores, which were strongly related to the thermal conductivity of the film, were observed in each YSZ grain. The pores are aligned in the <110> direction in the (111) plane and distributed across {11 4 ̄ } planes in T-grains, and aligned in the [ 1 ̄ 10] and the [001] directions in the (110) plane, and distributed across the (001) and ( 1 ̄ 10) planes in D-grains.

Phase transformation and bond coat oxidation behavior of EB-PVD thermal barrier coating

Thermal barrier coating, consisting of an electron beam physical vapor deposited partially stabilized zirconia (PSZ, 7 wt.%Y 2O 3) and a sputtered NiCrAlY bond coat, was investigated by thermal cycling at 1050 °C in air. Experimental characterization was conducted using X-ray diffraction analysis and scanning electron microscopy equipped with energy dispersive analytical X-ray spectroscopy. The lattice parameters of the tetragonal phase were determined as a function of thermal cycles. It was found that the c/ a ratio increases with thermal cycling, correspondingly to a decrease in the content of Y 2O 3 of the tetragonal phase. The nonequilibrium tetragonal phase (T′) of the PSZ slowly decomposed to tetragonal phase with relatively low Y 2O 3 content and cubic phase. After 300 cycles small amount of monoclinic phase was observed, which resulted from the tetragonal to monoclinic phase transformation during cooling. Al 2O 3 formed preferentially along the bond and top coat interface. After 200 cycles the thermally grown oxide (TGO) was very thin and consisted of only Al 2O 3. With Al-depletion in the bond coat, internal oxidation occurred and some other oxides such as NiO and Ni(Cr,Al) 2O 4 spinels were observed in the TGO near the bond coat.

Solid-state n.m.r. studies of crystalline phases in gel-spun ultrahigh molecular weight polyethylene

Gel-spun ultrahigh molecular weight polyethylene (UHMWPE) was examined by advanced solid-state 13C n.m.r. techniques to extract detailed information on the morphology and nature of the crystalline phases. Two partially overlapping resonances separated by 1.5 ppm in the 13C magic angle spinning n.m.r. spectrum have been assigned to monoclinic and orthorhombic crystalline phases. To analyse better the small amount of monoclinic phase, a 13C chemical shift filter was employed to suppress partially the dominant orthorhombic signal. The monoclinic phase exhibits a slightly smaller chemical shielding anisotropy of 27 ppm with chemical shift principal tensor values of 50, 36.5 and 16 ppm as compared to a shielding anisotropy of 30 ppm and principal tensor values of 50, 35.5 and 13 ppm for the orthorhombic phase. Additionally, a minor fraction of interface was detected arising from heterogeneous molecular packing. Both crystalline phases reveal an extremely high degree of order, with 〈 p 2〉 around 0.94. Whereas the conformations of the chains in the non-crystalline regions of both gel-spun and melt-spun polyethylene are alike, the mobility of the former is largely reduced. The morphology of UHMWPE is compared with that of melt-spun polyethylene.

Microstructure and Superconductivity in Bi–Sr–Ca–Cu–O System Doped with Pb and Sb

A series of samples BixPbySb0.1Sr2Ca2CuzOw has been produced by two methods. X-ray diffraction patterns revealed that there was a nearly single 2223 phase with a small amount of monoclinic phase in both two kinds of samples. The samples made by the oxalate coprecipitation technique had TCO=102 K. The A.C. magnetic susceptibility showed only one sharp transition at 110 K. For samples prepared by a mixture of powders, the electrical resistance began to drop at 140 K, reaching zero at 92 K. Their A.C. magnetic susceptibility showed sharp transition at 135 K, and no transition at 110 K. The monoclinic particles were segregated on the surface of the samples. The intergrowth of 2223 and monoclinic phases at their boundaries caused the partial distortion of the 2223 phase. The distorted 2223 phase might be responsible for the 130 K superconductivity.

The 130 K High-T c superconductor in the system Bi-Sr-Ca-Cu-O doped with Sb and Pb

A nearly pure 2223 phase of the ceramic superconductor Bi1.8Pb0.3Sb0.1Sr2Ca2Cu3O10−δ was obtained by solid-state reaction in air. The samples showed a semiconducting behavior when the temperature was higher than 140 K. The electrical resistance began to drop at 140 K and went to zero at 92 K. Their a.c. magnetic susceptibility showed two transitions at 130 and 89 K, but the 110 K transition was absent. These transitions were stable during cycling for three times from 77 K to room temperature. X-ray diffraction revealed that there was no 2212 or 2201 phase in these samples but only a small amount of monoclinic phase before and after cycling from 77 K to room temperature. SEM images showed that the grains of the monoclinic phase segregated on the surface of the sample and at the grain boundaries inside the sample, which is the reason for the sample's poor superconductivity and the decrease in zero resistance. Evidence from TEM and SEM equipped with a wavelength dispersive meter indicated distortion of the 2223 phase. These distorted 2223 crystals may be responsible for the 130 K superconductivity.