High temperature stiffening of ferroelastic LaCoO3

The cyclic ferroelastic hysteretic behavior of pure LaCoO₃ perovskite ceramic has been studied at different temperatures in four point bending. The stress-strain deformation behavior of LaCoO₃ was analyzed both in the term of the maximum stress in the cycle and in terms of the temperature used when the cyclic testing was performed. The characteristics of the stress-strain hysteresis loops, such as hysteresis loop area and irreversible strain, as well as effective Young’s modulus, were analyzed, and it was established that both the loading and the temperature history have a significant influence on the mechanical behavior of LaCoO₃. Young’s modulus values are reported to be much higher in the 700–900 °C temperature range as compared to the measurements performed in the RT-400 °C temperature range.     

The study of domain walls in Pb3(PO4)2 ferroelastic crystals

A ferroelastic domain between two domain walls do not have arbitrary thickness. There can be a minimum thickness which satisfies the geometrical boundary condition. In our study we suggest the possible minimum thickness of domain between two domain walls. The calculated thickness is compared with the observed thickness by TEM.     

Ferroelectric and ferroelastic phase transitions in (CH3NH3)3Sb2Br9 crystals

(CH₃NH₃)₃Sb₂Br₉ crystals were studied by pyroelectric method in the temperature range 10 - 200 K. Pyroelectric measurements revealed reversal spontaneous polarization below 141 K along the a-axis. The optical observations showed that MABA possesses ferroelastic domains in all low temperature phases.     

Structural phase transitions to the state with anomalously high-ionic conductivity in some perroelectric and ferroelastic crystals of the bisulpate group

The temperature dependences of the conductivity CsHSO₄, CsHSeO₄, RbHSO₄, RbHSEO₄, and NH₄HSO₄ have been measured and optical investigation was also made. It was found that the high temperature phase transitions in CsHSO₄, CsHSeO₄, and RbHSeO₄ at 413, 400 and 446 K, respectively are the transitions to the superionic state with 6'7 10^-30hm^-1.cm^-1. Some pecularities of these phase transitions are reported.     

Ferroelectricity and phase transitions in highly deuterated NH4HSeO4 crystals

Investigations of dielectric and pyroelectric properties as well as domain structure of 70% deuterated ammonium hydrogen selenate crystals have been carried out. Physical properties of 70% dauterated crystals grown in 12 phase differ considerably from that grown in P2₁2₁2₁ phase. Dielectric anomaly is observed that the paraelectric-incommensurate phase transition.     

Linear birefringence studies on the ferroelastic phase transition in betaine borate crystal

Linear birefringence studies were performed for the BBO crystal in the temperature range of 120-300 K. The linear birefringence changes induced by the ferroelastic phase transition at about 145 K were analysed and the critical index β was determined. The layered ferroelastic domain structure with domain walls oriented along the c- and a-axis was observed on the b-plate.     

High temperature monoclinic-to-tetragonal phase transition in magnesium doped lanthanum ortho-niobate

Magnesium doped lanthanum ortho-niobate (La_0.98Mg_0.02NbO₄) was prepared by the molten salt synthesis method. X-ray diffraction and dilatometry methods were used to study high temperature behavior of the ceramic material. Special attention was paid to the phase transition between the monoclinic and tetragonal phases. The values of spontaneous strain on the basis of unit cell parameter, obtained by Rietveld refinement, have been calculated as well as Landau order parameter. The thermal expansion coefficient (TEC) of La_0.98Mg_0.02NbO₄ was determined to be 12×10^?6 1/K and 8×10^?6 1/K below and above 500 °C, respectively.     

High internal phase emulsion as reaction medium for precipitating brushite crystals

This present work was aimed at fabrication of brushite crystals using oil-in-water high internal phase emulsion as a reaction medium. The oil phase of more than 75 wt.% was dispersed in the continuous aqueous phase. Due to the high oil volume fraction, the oil droplets were no longer spherical but were squeezed to take the shape of polyhedral. The morphology of the crystals was influenced by the structure of the emulsion and precursor concentration. The crystals were subjected to cytotoxicity test to ensure their compatibility with synoviocytes, which are cells that line the knee joints of rabbits. The crystals were able to sustain the cells for 5 days, which manifest their potential as osteoconductive coatings.     

Observation of the ferroelastic domain structure near the phase transition point

Temperature and time dependences of the ferroelastic domain structure were observed near the ferroelastic phase transition temperature in [N(CH₃)₄]₂ZnBr₄ single crystal. It was, found that the domain structure reaches a metastable state within about 20sec after quenching. The domain size increases with decreasing temperature.     

Conversion of MAX phase single crystals in highly porous carbides by high temperature chlorination

We show that combining high temperature chlorination with the chemical sensitivity of the A-atom planes of single crystals of some nano-lamellar MAX phases allows one to synthesize highly porous and electrically conducting carbides. Focusing on the case of porous Cr₃C₂, we present the dependence of the layer morphology, structure and formation kinetics on processing parameters such as temperature and time. The determination of the Raman signature of Cr₃C₂ and Cr₇C₃ allows us to follow the creation and elimination of the various phases as a function of processing time. Electrical resistivity and magnetoresistance data versus temperature and magnetic field are also presented and analyzed.     

Study of the phase transitions to the incommensurate phase in (NH4)2BeF4 (AFB) crystals

Specific heat high resolution data for AFB crystals are presented. The effect of SO₄²-ions impurities and γ-irradiation upon the hysteresis phenomena in AFB crystals is discussed.     

Low-frequency acoustic study of ferroelastic phase transitions in Ba2NaNb5O15

The peculiarities of low-frequency internal friction near the first order low-temperature (110 K) and second order high-temperature (573 K) phase transitions in improper Ba₂NaNb₅O₁₅ ferroelastic were studied. A large and wide internal friction peak and diffused step-like change in the temperature dependence of shear modulus were also observed within an incommensurate phase between these two phase transitions.     

塑性相结合刚玉复合砖的高温性能

通过设定高炉使用条件 ,将塑性相结合刚玉复合砖与现在高炉使用的刚玉莫来石砖及棕刚玉碳化硅砖在同等实验条件下进行了高温性能的比较。结果表明 :塑性相结合刚玉复合砖的结构致密 ,高温抗折强度高 ;而且在高温还原气氛下 ,其基质中的Si可与C和N2 反应 ,生成具有良好抗炉渣、铁水和碱金属侵蚀能力的碳化物和氮化物 ,并填充表面的间隙 ,形成一个良好的防护层 ,因此其抗侵蚀性能优于棕刚玉碳化硅砖和刚玉莫来石砖。     

High temperature crystallographic and low temperature magnetic phase transitions in Fe doped Sr2RuMnO6

Fe doped Sr₂RuMnO₆ (SRMO) double perovskites (Sr₂RuMn_1-xFe_xO₆, x = 0, 0.1, 0.2 and 0.3) were prepared by solid-state route. Both x-ray diffraction and Raman spectroscopy were performed to investigate the crystal structure of the synthesized double perovskites. Rietveld refinement of the x-ray diffraction patterns confirmed a phase transition from tetragonal to cubic space group as a function of doping concentration of iron. Raman spectroscopy at room temperature and group theory analysis revealed the phonon modes associated with the space group of the samples. The temperature dependent Raman spectroscopy showed an anharmonic behaviour of the phonon modes of the Fe doped SRMO samples. The temperature evolution of the phononic modes in the range of 300 K–620 K is predominantly influenced by the lattice degrees of freedom. The presence of several oxidation states Mn (2⁺, 3⁺ and 4⁺) and Fe (3⁺ and 4⁺) was confirmed by an X-ray photoemission spectroscopy analysis of the highest doped sample (x = 0.3). The magnetic properties measurements showed that the samples were completely paramagnetic at room temperature. The samples exhibit antiferromagnetism at very low temperatures and we conclude that they exhibit ferrimagnetic ground state in the mid temperature region.     

臭菜抗氧化活性研究

为了研究臭菜提取物体外抗氧化活性,考察其对DPPH自由基和羟自由基活性的清除能力,并且与多种抗氧化剂进行对照研究。通过实验得出,臭菜提取物清除DPPH自由基活性的能力优于对香豆酸。结果表明,臭菜提取物具有很好的清除DPPH自由基和羟自由基活性的能力,是一种良好的天然抗氧化剂。     

微波高温固相法合成高纯磷酸盐的实验研究

研究了采用微波高温固相法快速合成高纯磷酸盐的工艺条件,与传统高温固相合成反应相比,磷酸三钙的合成时间比传统加热方式减少了50%,反应温度降低200℃;磷酸三钾的合成时间比传统加热方式减少了2/3,反应温度降低250℃。XRD分析结果显示磷酸盐结晶形态稳定。     

Ultra-low temperature sintering and temperature stable microwave dielectrics of phase pure AgMgVO4 ceramics

The present study systematically invesitgates the formation and microwave dielectric properties of novel AgMgVO₄ ceramics fabricated via the solid-state reaction method. The crystal structure of the ceramics is confirmed to be orthorhombic with a space Group of Pnma (62). A high relative density of 96.2% and an excellent combination of microwave dielectric properties with ε_r of ~14.89, Q×f of ~19,400 GHz, and τ_f of ~ ? 2.71 ppm/°C can be achieved for the ceramic sintered at 630 °C. The dielectric constant is mainly influenced by the relative density (porosity) and dielectric polarizability. The Q×f is controlled by the microstructure, packing fraction, and lattice energy, which are also highly related to the unit-cell volume. A smaller unit-cell volume leads to a high Q×f. Variation of the τ_f is strongly correlated to the bond valence of the specimen. Furthermore, the ceramic exhibits good chemical compatibility with aluminum electrodes and is demonstrated as a potent substrate for a band-pass filter with a center frequency of 3.5 GHz. These findings show a great promise for ultra-low temperature co-fired ceramic applications at high frequencies.     

High pressure–high temperature growth of diamond crystals using split sphere apparatus

An overview of the application of crystal growth fundamentals in the high pressure–high temperature production of diamond by solvent/catalyst technique is presented. The process, also called temperature gradient process, makes use of a molten catalyst to dissolve carbon from a source (graphite or diamond powder) and transport the dissolved carbon to a growth site where they precipitate on a diamond seed. The pressure and temperature requirements for the process are generally around 5.0–6.5 GPa and 1300–1700 °C, depending on the chemistry of the solvent used and the desired crystal geometry. In spite of major progress in the science and technology of diamond growth, large scale commercial production of diamonds single crystals for jewelry or electronic applications has not been feasible until recently. This has been mainly due to the substantial cost associated with the presses needed, and the difficulties in controlling the growth parameters and catalyst chemistry. The recent developments in the commercial production of diamond single crystals utilizing the Split Sphere pressurization apparatus are discussed.     

Dislocation microstructure of 4H-SiC single crystals plastically deformed around the transition temperature

4H-SiC specimens were plastically deformed by basal slip at temperatures between 800 °C and 1300 °C. Samples were investigated by means of transmission electron microscopy and high-resolution techniques. The accepted transition temperature (1030 °C) was found not to be actually so well defined since the two mechanisms were operating together between 1000 °C and 1100 °C. Dissociation of basal dislocations takes place over the entire temperature range investigated, having a different influence on each regime. In the high temperature regime, after dissociation the two partials slip together in the basal plane fringing a stacking fault. We have determined the dissociation width, obtaining a stacking fault energy of 20 ± 5 mJ/m². However, below the transition temperature the difference in mobility of the partials and the low stacking fault energy allow the leading partial to glide alone. We discuss the consequences of this finding for the crystal structure (cubic bands nucleation) and mechanical behaviour (high work-hardening rate).     

The temperature dependence of the absorption edge in Bismuth vanadate crystals (BiVO4)

The temperature dependence of the absorption edge in bismuth vanadate single crystal was measured, and it has turned out that the absorption edge shifts towards the longer wave-length side with increasing temperature.