• Korean Journal of Crystallography
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• v.14 no.1
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• pp.13-15
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• 2003

For all primitive centric space groups in the triclinic, monoclinic and orthorhombic systems, either phase 0 or π can be allocated to three different kinds of reflections in order to specify the origin at one of the eight centers of symmetry. and the same holds for all primitive acentric space groups belonging to the point group 222. If these phased reflections are used as a basic set, more and more phased reflections with better accuracy could emerge in the process of direct methods.

• Journal of Technologic Dentistry
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• v.33 no.4
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• pp.323-329
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• 2011

Purpose: This study was conducted to examine the phase transition according to the zirconia surface treatment. Methods: The specimens were divided to four groups. The first group was sintered at $1,500^{\circ}C$ and ground; the second group was sintered at $700^{\circ}C$, ground, and sintered at $1,500^{\circ}C$; the third group was sintered at $1,500^{\circ}C$, ground, and $110{\mu}m$-sandblasted; and the fourth group was sintered at $1,500^{\circ}C$, ground, $110{\mu}m$-sandblasted, treated with 9.5% hydrofluoric acid, and ultrasonic cleaner-washed for two minutes. The monoclinic fractions were measured, and the surface was observed via SEM. Results: The monoclinic fraction was $0.13{\pm}0.19%$ in the control group Zr1, $1.91{\pm}0.15%$ in the experimental group Zr2, $7.71{\pm}0.34%$ in Zr3, and $8.39{\pm}0.25%$ in Zr4. On the surface, the phase transition hardly occurred in the control group Zr1, but it increasingly occurred in the experimental groups Zr3 and Zr4. Conclusion: The monoclinic fraction was high in the experimental groups Zr3 and Zr4. The phase transition did not occur in the control group, but increasingly occurred in the experimental groups.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.5
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• pp.205-211
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• 2022

The Granule Spray in Vacuum (GSV) process is a method of forming a dense nanostructured ceramic coating film by spraying ceramic granules on a substrate at room temperature in a vacuum. In the Granule Spray, the granules made by agglomerating particles with the size from submicrometer to micrometer can be sprayed into the substrate. Once the granules were squashed upon collision with the substrate, they become several dozens of nanometer-sized crystals in vacuum process. The zirconia of the monoclinic phase transform into tetragonal phase at 1150℃. At this time, its volume is changed by about 6.5 %. For this reason, it is widely held that it is difficult to acquire a compact of monoclinic zirconia sinter. In this study, the effect of particle treatment temperature and standoff distance on the substrate of zirconia granules were investigated in GSV. Also, particle treatment temperature, standoff distance, coating efficiency, and microstructure of the film were considered in forming the monoclinic zirconia coating film in GSV without any heating process. The deposited films exhibited monoclinic zirconia phase without any other detectable phase by X-ray diffractometer (XRD).

• Proceedings of the Korean Magnestics Society Conference
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• 2011.06a
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• pp.7-8
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• 2011

Basically, the lattice mismatch between film and substrate can make those BiFeO3(BFO) films distorted with strain structure. BFO phase can be stabilized on LaAlO3(LAO) represents the example of a multiferroic with giant axial ratio. Its crystal structure is not strictly tetragonal, but tetragonal with a slight monoclinic distortion and related to the rotation of the oxygen octahedra. In this study, we show that phases with a tetragonal-like epitaxial BFO films can indeed be ferroelectric and also can be stabilized via epitaxial growth onto LAO. Recent reports on epitaxial BFO films show that the crystal structure changes from nearly rhombohedral ("R-like") to nearly tetragonal("T-like") at strains exceeding approximately -4.5%, with the "T-like" structure being characterized by a highly enhanced c/a ratio. While both the "R-like" and the "T-like" phases are monoclinic, our detailed x-ray diffraction results reveal asymmetry change from MA and MC type, respectively. By applying additional strain or by modifying the unit cell volume of the film by substituting Ba for Bi, the monoclinic distortion in the "T-like" MC phase is reduced, i.e. the system approaches a true tetragonal symmetry. There are two different M-H loops for $Bi_{1-x}Ba_xFeO_{3-{\delta}}$(BBFO) and BFO films on SrTiO3(STO) & LAO substrates. Along with the ferroelectric characterization, these magnetic data indicate that the BFO phase stabilized on LAO represents the first example of a multiferroic with giant axial ratio. However, there is a significant difference between this phase and other predicted ferroelectrics with a giant axial ratio: its crystal structure is not strictly tetragonal, but tetragonal with a slight monoclinic distortion. Therefore, in going from bulk to highly-strained films, a phase sequence of rhombohedral(R)-to-monoclinic ["R-like" MA-to-monoclinic, "T-like" MC-to-tetragonal (T)] is observed. This sequence is otherwise seen only near morphotropic phase boundaries in lead-based solid-solution perovskites (i.e. near a compositionally induced phase instability), where it can be controlled by electric field, temperature, or composition. Our results show that this evolution can occur in a lead-free, stoichiometric material and can be induced by stress alone. Those major results are summarized as follows ; 1) Ba-doping increases the unit cell volume, 2) BBFO on LAO can be fully strained up to x=0.08 as a strain limit (Fig. 1), 3) P(E) & M(H) properties can be tuned by the variation of composition, strain, and film thickness.

• Korean Journal of Materials Research
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• v.23 no.6
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• pp.329-333
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• 2013

The structural phase transformations of $0.7Pb(Mg_{1/3}Nb_{2/3})O_3-0.3PbTiO_3$ (PMN-0.3PT) were studied using high resolution x-ray diffraction (HRXRD) as a function of temperature and electric field. A phase transformational sequence of cubic (C)${\rightarrow}$tetragonal (T)${\rightarrow}$rhombohedral (R) phase was observed in zero-field-cooled conditions; and a $C{\rightarrow}T{\rightarrow}$monoclinic $(M_C){\rightarrow}$ monoclinic ($M_A$) phase was observed in the field-cooled conditions. The transformation of T to $M_A$ phase was realized through an intermediate $M_C$ phase. The results also represent conclusive and direct evidence of a $M_C$ to $M_A$ phase transformation in field-cooled conditions. Beginning from the zero-field-cooled condition, a $R{\rightarrow}M_A{\rightarrow}M_C{\rightarrow}T$ phase transformational sequence was found with an increasing electric field at a fixed temperature. Upon removal of the field, the $M_A$ phase was stable at room temperature. With increasing the field, the transformation temperature from T to $M_C$ and from $M_C$ to $M_A$ phase decreased, and the phase stability ranges of both T and $M_C$ phases increased. Upon removal of the field, the phase transformation from R to $M_A$ phase was irreversible, but from $M_A$ to $M_C$ was reversible, which means that $M_A$ is the dominant phase under the electric field. In the M phase region, the results confirmed that lattice parameters and tilt angles were weakly temperature dependent over the range of investigated temperatures.

• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1147-1158
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• 1994

From Zr(O-nC3H7)4-H2O-C2H5OH-HNO3 starting solutions, MgO-doped stabilized zirconia fibers with varying content of MgO (10~18 mol%) from different MgO sources were fabricated by sol-gel method. The MgO sources used are magnesium nitrate hexahydrate, magnesium acetate tetrahydrate, and magnesium ethylate. The phase transformation studies of a drawn MgO-ZrO2 fiber were carried out using X-ray diffraction, IR spectroscopy, and Raman spectroscopy. The microstructure, tensile strength, and microporosity of fibers were investigated using SEM, tensile strength test, and microporosimeter. Although various MgO sources such as magnesium nitrate, acetate, and ethylate were used, the crystallization behavior of MgO-ZrO2 fibers at different temperatures could be summarized as follows: CubiclongrightarrowMetastable TetragonallongrightarrowMonocliniclongrightarrowCoexistence of Monoclinic and CubiclongrightarrowCubic(trace of monoclinic). At 150$0^{\circ}C$, the phase transformation of MgO-ZrO2 fibers shows the following change depending on the amount of MgO[Mg(NO3)2.6H2O]: At 10 mol%, both monoclinic and cubic phase coexist, at 12 mol%, monoclinic phase decreases rapidly, and then at 14 mol%, only cubic phase remains. When the MgO-ZrO2 fibers containing 12 mol% magnesium nitrate were heated at 80$0^{\circ}C$ for 1hr, average tensile strength of fibers is 4.0 GPa at diameters of 20 to 30 ${\mu}{\textrm}{m}$. As the heat-treatment temperatures increase to 100$0^{\circ}C$ for 1 hr, tensile strength of MgO-ZrO2 fibers decreases rapidly to 0.7 GPa.

• Journal of Magnetics
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• v.21 no.2
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• pp.168-172
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• 2016

$BiMnO_3$ has been a promising candidate as a magnetoelectric multiferroic while there have been many controversial reports on its ferroelectricity. The detailed analysis of its film growth, especially the growth of thin film having monoclinic symmetry has not been reported. We studied the effect of miscut angle, the substrate surface, and film thickness on the symmetry of $BiMnO_3$ thin film. A flat $SrTiO_3$ (110) substrate resulted in a thin film with three domains of $BiMnO_3$ and 1 degree miscut in the $SrTiO_3$ (110) substrate resulted in dominant domain preference in the $BiMnO_3$ thin film. The larger miscut resulted in a nearly perfect detwinned $BiMnO_3$ film with a monoclinic phase. This strong power of domain selection due to the step edge of the substrate was efficient even for the thicker film which showed a rather relaxed growth behavior along the $SrTiO_3$ [1-10] direction.

• Korean Journal of Materials Research
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• v.23 no.10
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• pp.543-549
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• 2013

The purpose of this paper was to investigate the effect of a high-energy milling (HEM) process on the particle morphology and the correlation between a thermal treatment and tetragonal/monoclinic nanostructured zirconia powders obtained by a precipitation process. To eliminate chloride residue ions from hydrous zirconia, a modified washing method was used. It was found that the used washing method was effective in removing the chloride from the precipitated gel. In order to investigate the effect of a pre-milling process on the particle morphology of the precipitate, dried $Zr(OH)_4$ was milled using a HEM machine with distilled water. The particle size of the $Zr(OH)_4$ powder exposed to HEM reduced to 100~150 nm, whereas that of fresh $Zr(OH)_4$ powder without a pre-milling process had a large and irregular size of 100 nm~1.5 ${\mu}m$. Additionally, modified heat treatment process was proposed to achieve nano-sized zirconia having a pure monoclinic phase. It was evident that two-step calcining process was effective in perfectly eliminating the tetragonal phase, having a small average particle of ~100 nm with good uniformity compared to the sample calcined by a single-step process, showing a large average particle size of ~300 nm with an irregular particle shape and a broad particle size distribution. The modified method is considered to be a promising process for nano-sized zirconia having a fully monoclinic phase.

• Journal of the Korean Ceramic Society
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• v.36 no.7
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• pp.762-766
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• 1999

The crystal structure of A2+(Mg1/3Nb2/3)O3,(A2+=Sr2+ and Ca2+)ceramics was studied usig X-ray diffraction (XRD) and high resolution transmission electrion microscopy(HRTEM). Ba(Mg1/3Nb2/3)O3 (SMN) has the 1:2 ordered monoclinic structure which has the anti-phase tilt of octahedra. The type of tilting in SMN was considered to be a$^{\circ}$a$^{\circ}$c- or a­a­c$^{\circ}$ Ca(Mg1/3Nb2/3)O3 (CMN) also has the 1:2 ordered monoclinic structure which was distorted by the anti-phase tilt or in-phsae tilt of octahedra. A unit cell containing both the in-phase tilt axis and anti-phase tilt axis was not observed in the CMN. Therefore CMN has the mixed phase consisting of the 1:2 ordered monoclinic phase with anti-phase tilt of octahedra and the one with in -phase tilt of ocatahedra,. The anti-parallel shift of cation was also observed in the CMN.

• Korean Journal of Materials Research
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• v.22 no.7
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• pp.342-345
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• 2012

The dielectric properties and phase transformation of poled <001>-oriented $Pb(Mg_{1/3}Nb_{2/3})O_3-x%PbTiO_3$(PMN-x%PT) single crystals with compositions of x = 20, 30, and 35 mole% are investigated for orientations both parallel and perpendicular to the [001] poling direction. An electric-field-induced monoclinic phase was observed for the initial poled PMN-30PT and PMN-35PT samples by means of high-resolution synchrotron x-ray diffraction. The monoclinic phase appears from $-25^{\circ}C$ to $100^{\circ}C$ and from $-25^{\circ}C$ to $80^{\circ}C$ for the PMN-30PT and PMN-35PT samples, respectively. The dielectric constant (${\varepsilon}$)-temperature (T) characteristics above the Curie temperature were found to be described by the equation$(1/{\varepsilon}-1/{\varepsilon}_m)^{1/n}=(T-T_m)/C$, where ${\varepsilon}_m$ is the maximum dielectric constant and $T_m$ is the temperature giving ${\varepsilon}_m$, and n and C are constants that change with the composition. The value of n was found to be 1.82 and 1.38 for 20PT and 35PT, respectively. The results of mesh scans and the temperature-dependence of the dielectric constant demonstrate that the initial monoclinic phase changes to a single domain tetragonal phase and a to paraelectric cubic phase. In the ferroelectric tetragonal phase with a single domain state, the dielectric constant measured perpendicular to the poling direction was dramatically higher than that measured in the parallel direction. A large dielectric constant implies easier polarization rotation away from the polar axis. This enhancement is believed to be related to dielectric softening close to the morphotropic phase boundary.