Multifunctional role of dysprosium in HfO2: stabilization of the high temperature cubic phase, and magnetic and photoluminescence properties

2017 ◽  
Vol 19 (29) ◽  
pp. 18957-18967 ◽  
Author(s):  
Sandeep Kumar ◽  
S. B. Rai ◽  
Chandana Rath
Keyword(s):  
High Temperature ◽  
Hafnium Oxide ◽  
Room Temperature ◽  
Cubic Phase ◽  
Photoluminescence Properties ◽  
Crystalline Structures

Hafnium oxide (HfO2) can exist in different crystalline structures such as monoclinic at room temperature, tetragonal at 1700 °C and cubic at 2600 °C.

High-temperature X-ray powder diffraction study of the tetragonal-cubic phase transition in nanocrystalline, compositionally homogeneous ZrO2–CeO2 solid solutions

2008 ◽  
Vol 23 (S1) ◽  
pp. S70-S74 ◽  
Author(s):  
L. M. Acuña ◽  
R. O. Fuentes ◽  
D. G. Lamas ◽  
I. O. Fábregas ◽  
N. E. Walsöe de Reca ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Temperature ◽  
Powder Diffraction ◽  
Solid Solutions ◽  
Tetragonal Phase ◽  
Room Temperature ◽  
Cubic Phase ◽  
X Ray ◽  
First Order

Crystal structure of compositionally homogeneous, nanocrystalline ZrO2–CeO2 solutions was investigated by X-ray powder diffraction as a function of temperature for compositions between 50 and 65 mol % CeO2. ZrO2-50 and 60 mol % CeO2 solid solutions, which exhibit the t′-form of the tetragonal phase at room temperature, transform into the cubic phase in two steps: t′-to-t″ followed by t″-to-cubic. But the ZrO2-65 mol % CeO2, which exhibits the t″-form, transforms directly to the cubic phase. The results suggest that t′-to-t″ transition is of first order, but t″-to-cubic seems to be of second order.

Stabilization of high temperature hexagonal phase of SrAl2O4 at room temperature: role of ZnO

2014 ◽  
Vol 43 (14) ◽  
pp. 5309 ◽  
Author(s):  
V. P. Singh ◽  
S. B. Rai ◽  
H. Mishra ◽  
Chandana Rath
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
Hexagonal Phase

The Role of Callistemon Fruits and Infructescences in Protecting Seeds from Heat in Fires

1998 ◽  
Vol 46 (2) ◽  
pp. 235 ◽  
Author(s):  
Claire L. Brown ◽  
Robert J. Whelan
Keyword(s):  
High Temperature ◽  
Seed Germination ◽  
High Intensity ◽  
Room Temperature ◽  
Seed Viability ◽  
Protective Role ◽  
Percentage Germination ◽  
Low Intensity ◽  
Australian Plant

A number of Australian plant species tolerate fires because seeds are protected in woody fruits and are released after fire, but there is little information about the role of the fruit, or a collection of fruits, in protecting seed from the heat of a fire. This study examined the effects of various temperatures applied to infructescences of Callistemon citrinus (Curtis) Skeels on seed germination. The protective role of the dense collection of fruits in maintaining seed viability was tested by experimentally ‘thinning’ infructescences before heating. Heating of infructescences significantly increased the percentage of seeds germinating from less than 20% at room temperature to over 35% at 200˚C, but caused a decline, with further temperature increase to 800˚C. There was a slight but statistically significant increase in the percentage germination of seeds from thinned infructescences. Increased germination following exposure to high temperature may be a way for a plant to synchronise germination after high-intensity fire, while spreading it out if seeds are released in the absence of fire or after a low-intensity fire.

THERMAL TRANSFORMATIONS OF STILBITE

1966 ◽  
Vol 3 (3) ◽  
pp. 351-366 ◽  
Author(s):  
F. Aumento
Keyword(s):  
High Temperature ◽  
Amorphous Silica ◽  
Room Temperature ◽  
Cell Parameter ◽  
Maximum Temperature ◽  
Cubic Phase ◽  
Crystal Data ◽  
Thermal Transformations ◽  
Cell Parameters ◽  
Metastable Form

Stilbite samples from two localities were examined. Preliminary D.T.A. and T.G.A. investigations to 1 400 °C were followed by high temperature diffractometry. Debye–Scherrer and Guinier techniques were used to study cooled samples, Diffractometer and single crystal data were processed with a computer to calculate cell parameters and thermal expansion.Stilbite changes to a metastable form of epistilbite at 145 °C. At 240 °C and 470 °C epistilbite shows two modifications followed by gradual destruction. Semi-amorphous silica formed by this process yields β-cristobalite and anorthite at 920 °C. Anorthite is replaced, at 1 340 °C, by an unidentified cubic phase. β-Cristobalite is found to be metastable down to room temperature; its room temperature cell parameter "a" is inversely proportional to the maximum temperature of annealment.

Reconstructive phase transition in (NH4)3TiF7accompanied by the ordering of TiF6octahedra

2014 ◽  
Vol 70 (6) ◽  
pp. 924-931 ◽  
Author(s):  
Maxim Molokeev ◽  
S. V. Misjul ◽  
I. N. Flerov ◽  
N. M. Laptash
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Room Temperature ◽  
Parent Phase ◽  
High Temperature Phase ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Large Rotations ◽  
Fourfold Axis

An unusual phase transitionP4/mnc→ Pa\bar 3 has been detected after cooling the (NH4)3TiF7compound. Some TiF6octahedra, which are disordered in the room-temperature tetragonal structure, become ordered in the low-temperature cubic phase due to the disappearance of the fourfold axis. Other TiF6octahedra undergo large rotations resulting in huge displacements of the F atoms by 1.5–1.8 Å that implies a reconstructive phase transition. It was supposed that phasesP4/mbmand Pm\bar 3m could be a high-temperature phase and a parent phase, respectively, in (NH4)3TiF7. Therefore, the sequence of phase transitions can be written as Pm\bar 3m →P4/mbm→P4/mnc→ Pa\bar 3. The interrelation between (NH4)3TiF7, (NH4)3GeF7and (NH4)3PbF7is found, which allows us to suppose phase transitions in relative compounds.

Phase relations in the Ba–Sr–Co–Fe–O system at 1273 K in air

2009 ◽  
Vol 42 (2) ◽  
pp. 153-160 ◽  
Author(s):  
Zhèn Yáng ◽  
Ashley S. Harvey ◽  
Anna Infortuna ◽  
Ludwig J. Gauckler
Keyword(s):  
High Temperature ◽  
Solid State ◽  
Solid State Reaction ◽  
Room Temperature ◽  
Solid State Reaction Method ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Reaction Method ◽  
X Ray

Selected compositions of the Ba–Sr–Co–Fe–O system were synthesized from powders by the solid-state reaction method. Samples were equilibrated at 1273 K for 36 000 s in air. The resulting powders were characterized by X-ray diffraction (XRD) at room temperature and by high-temperaturein situXRD. The phases present in the BaxSr1−xCoyFe1−yO3−δsystem are outlined for 1273 K in air. For most of the quaternary compositions, the cubic perovskite is formed, except for the compositions withx= 1 (excludingy= 0.4),y= 1 andx,y= 0.8, where the phases mainly show hexagonal distortions, andx, y= 0, for which a predominant cubic phase is mixed with other phases.

CsH2PO4: Electrolyte for Intermediate Temperature Fuel Cells

2011 ◽  
Vol 239-242 ◽  
pp. 2492-2498
Author(s):  
Hock Chee Teo ◽  
Loh Kee Shyuan ◽  
Abu Bakar Mohamad ◽  
Abdul Amir Hassan Kadhum
Keyword(s):  
High Pressure ◽  
Fuel Cells ◽  
High Temperature ◽  
Title Compound ◽  
Room Temperature ◽  
Review Paper ◽  
Cubic Phase ◽  
Dihydrogen Phosphate ◽  
Thermal Event ◽  
Saturated Atmosphere

This review paper discusses the temperature behavior and thermal event of cesium dihydrogen phosphate (CsH2PO4) in both ambient and high pressure atmosphere. A complete transition from the room-temperature to a high-temperature of CsH2PO4 (monoclinic to cubic phase) occurs between 230 to 240 °C, even in the absence of humid conditions and the superprotonic transition precedes the onset of the dehydration/chemical decomposition of the title compound. Decomposition or dehydration can be avoided by either keeping the sample under a H2O-saturated atmosphere, or subjecting the sample to a pressure of 1.0 ± 0.2 GPa.

ABOUT HEAT CAPACITY OF TITANIUM CARBIDE TiCx

2019 ◽  
pp. 56-66
Author(s):  
I. Khidirov ◽  
V. V. Getmanskiy ◽  
A. S. Parpiev ◽  
Sh. A. Makhmudov
Keyword(s):  
Heat Capacity ◽  
High Temperature ◽  
Titanium Carbide ◽  
Temperature Dependence ◽  
Carbon Concentration ◽  
Room Temperature ◽  
Thermodynamic Characteristics ◽  
Liquid Nitrogen Temperature ◽  
Analysis Data ◽  
Thermal Excitation

This work relates to the field of thermophysical parameters of refractory interstitial alloys. The isochoric heat capacity of cubic titanium carbide TiCx has been calculated within the Debye approximation in the carbon concentration  range x = 0.70–0.97 at room temperature (300 K) and at liquid nitrogen temperature (80 K) through the Debye temperature established on the basis of neutron diffraction analysis data. It has been found out that at room temperature with decrease of carbon concentration the heat capacity significantly increases from 29.40 J/mol·K to 34.20 J/mol·K, and at T = 80 K – from 3.08 J/mol·K to 8.20 J/mol·K. The work analyzes the literature data and gives the results of the evaluation of the high-temperature dependence of the heat capacity СV of the cubic titanium carbide TiC0.97 based on the data of neutron structural analysis. It has been proposed to amend in the Neumann–Kopp formula to describe the high-temperature dependence of the titanium carbide heat capacity. After the amendment, the Neumann–Kopp formula describes the results of well-known experiments on the high-temperature dependence of the heat capacity of the titanium carbide TiCx. The proposed formula takes into account the degree of thermal excitation (a quantized number) that increases in steps with increasing temperature.The results allow us to predict the thermodynamic characteristics of titanium carbide in the temperature range of 300–3000 K and can be useful for materials scientists.

Sign in / Sign up

Export Citation Format

Share Document