Search

A new method is described to characterize the transformation kinetics of reconstructive systems at high temperatures using synchrotron X‐ray radiation, a quadrupole lamp furnace, and a detector capable of collecting a diffraction pattern of sufficient range in a minimal amount of time. Using this method, the activation energy for a reconstructive phase transformation in Dy2TiO5 was determined to be 149 kJ/mol. This value is more reasonable when compared with the uncertain values determined using conventional methods such as differential scanning calorimetry. In addition, the new method also provides higher quality data with improved time resolution, leading to better determination of fitted kinetic parameters. [ABSTRACT FROM AUTHOR]

Crystalline pure NaTi2(PO4)3 (NTP) powder was synthesized at 700°C using a simple and low energy, hybrid inorganic-organic, steric entrapment method. Sodium nitrite (NaNO2) and ammonium phosphate dibasic ((NH4)2HPO4) dissolved in water, whereas titanium (IV) isopropoxide (Ti[OCH(CH3)2]4) hydrolyzed in water. Ethylene glycol (HOCH2CH2OH) was used as a polymeric entrapper and hydrolysis of the Ti source was hindered by its dissolution in isopropyl alcohol. The resulting NTP powder was characterized by thermogravimetric analysis/ differential thermal analysis, X-ray diffractometry, scanning electron microscopy, specific surface area by Brunauer-Emmett-Teller nitrogen absorption, and particle size analysis. Furthermore, C, H, N were measured by the classical Pregl-Dumas method. The thermal expansion behavior in all {hkl} pole directions was also determined by in situ high-temperature X-ray diffraction using synchrotron radiation and was found to be in agreement with other published studies. [ABSTRACT FROM AUTHOR]

The thermal expansion of Dy2TiO5 in the hexagonal phase was evaluated and compared with the orthorhombic phase using in situ high-temperature X-ray diffraction. The crystal structure, volume changes before and after the transformation process, as well as the mechanism behind the thermal expansion behavior was determined and proposed. It was found that in the hexagonal phase, the thermal expansion was caused by the oxygen anions in the axial positions of the trigonal bipyramidal structure moving toward the central Ti atom. While expanding, the movement of these oxygen anions slows the expansion along the c-axis resulting in a decrease in α33 with temperature. Furthermore, a structural relationship between the orthorhombic and the hexagonal phases was proposed. [ABSTRACT FROM AUTHOR]

The thermal expansion of Dy2TiO5 in the hexagonal phase was evaluated and compared with the orthorhombic phase using in situ high-temperature X-ray diffraction. The crystal structure, volume changes before and after the transformation process, as well as the mechanism behind the thermal expansion behavior was determined and proposed. It was found that in the hexagonal phase, the thermal expansion was caused by the oxygen anions in the axial positions of the trigonal bipyramidal structure moving toward the central Ti atom. While expanding, the movement of these oxygen anions slows the expansion along the c-axis resulting in a decrease in α33 with temperature. Furthermore, a structural relationship between the orthorhombic and the hexagonal phases was proposed. [ABSTRACT FROM AUTHOR]

The thermal expansion behavior of the orthorhombic phase in the Ln2TiO5 (Ln = La, Nd, Gd, Dy, and Y) system was evaluated, using synchrotron X-ray diffraction from room temperature to approximately 1500°C in air. The components of the thermal expansion tensor were calculated from the refined d-spacings, using the program CTEAS. Subsequent analysis of the thermal expansion and crystallographic information revealed that the mechanism behind the thermal expansion was a result of strained trigonal-bipyramidal structures overcoming an energy barrier to become more relaxed. The temperature at which a significant shift in the trigonal-bipyramidal structure manifests was correlated with the size of the rare-earth cation that dictates the volume of the overall cell. Larger rare-earth cations with larger cell volumes allow more room for the trigonal-bipyramidal structures to easily relax. [ABSTRACT FROM AUTHOR]