Electrical and Dielectric Spectroscopic Characterization of Polycrystalline Dy2Si2O7

2012 ◽  
Vol 510-511 ◽  
pp. 194-200 ◽  
Author(s):  
Shahid Ameer ◽  
Asghari Maqsood
Keyword(s):  
High Temperature ◽  
Electrical Transport ◽  
Ac Conductivity ◽  
Orthorhombic Phase ◽  
Theoretical Models ◽  
Spectroscopic Characterization ◽  
Dielectric Parameters ◽  
Triclinic Phase ◽  
Electrical Conductivities ◽  
Phase Type

The compound Dy2Si2O7exists in two polymorphs, the low temperature triclinic phase (type B) and a high temperature orthorhombic phase (type E).The dc and ac electrical conductivities of E-Dy2Si2O7are measured in the temperature range 290-510 K and frequency range 1 kHz to 1 MHz . The dc electrical transport data are analyzed according to Motts variable-range hopping model. The disorder parameter (To) and density of states at fermi level are obtained. The ac conductivity σac(ω) is obtained through the dielectric parameters. The ac conductivity can be expressed as σac(ω) =B ωs, where s is slope and it decreases with increase in temperature. The conduction mechanism in the compound is discussed in low and high temperature regions in the light of theoretical models.

Synthesis, Structural, Electrical, Magnetic and Dielectric Spectroscopic Characterization of C-Er2Si2O7

2012 ◽  
Vol 17 ◽  
pp. 85-98 ◽  
Author(s):  
Shahid Ameer ◽  
Ahmad Faraz ◽  
Asghari Maqsood ◽  
Nasir M. Ahmad
Keyword(s):  
Electrical Transport ◽  
Ac Conductivity ◽  
Electrical Characterization ◽  
Magnetic Behavior ◽  
Spectroscopic Characterization ◽  
X Ray Diffraction ◽  
Spectroscopic Measurements ◽  
X Ray ◽  
Sintering Method

The Polymorphic Er2Si2O7Is Synthesized by Solid State Double Sintering Method. Structural and Morphological Characterizations Have Been Performed Using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The Electrical Characterization Has Been Performed by Two Probe Method as a Function of Temperature. the Dielectric Spectroscopic Measurements of Polymorphic Er2Si2O7Are Performed in the Temperature Range 300-555 K and Frequency Range 3 kHz to 1 MHz. the dc Electrical Transport Data Are Analyzed According to Mott’s Variable-Range Hopping. The ac Conductivity σac(ω) Is Obtained through the Dielectric Spectroscopic Measurements. the ac Conductivity Obeys Power Law which Can Be Expressed as σac (ω) = B ωs, where S Is Slope and it Determines the ac Electrical Transport Phenomenon. the ac Electrical Transport Data and its Variation with Temperature in this Rare Earth Formulation Are Well Discussed. the Magnetic Behavior of Synthesized Material Is Analyzed and Confirmed that Material Have Non-Magnetic Behavior with Coercivity (Hc) 842 Oe. while the Values of Magnetic Saturation (MS) and Remanace (Mr) Were Found in Range 3.90emu/g and 1.07emu/g.

scholarly journals Temperature dependence of hardness prediction for high-temperature structural ceramics and their composites

2021 ◽  
Vol 10 (1) ◽  
pp. 586-595
Author(s):  
Ruzhuan Wang ◽  
Dingyu Li ◽  
Weiguo Li
Keyword(s):  
High Temperature ◽  
Temperature Dependence ◽  
Material Design ◽  
Theoretical Models ◽  
Ceramic Composites ◽  
Basic Material ◽  
Experimental Measurements ◽  
Control Mechanisms ◽  
Oxide Ceramics ◽  
Structural Ceramics

Abstract Hardness is one of the important mechanical properties of high-temperature structural ceramics and their composites. In spite of the extensive use of the materials in high-temperature applications, there are few theoretical models for analyzing their temperature-dependent hardness. To fill this gap in the available literature, this work is focused on developing novel theoretical models for the temperature dependence of the hardness of the ceramics and their composites. The proposed model is just expressed in terms of some basic material parameters including Young’s modulus, melting points, and critical damage size corresponding to plastic deformation, which has no fitting parameters, thereby being simple for materials scientists and engineers to use in the material design. The model predictions for the temperature dependence of hardness of some oxide ceramics, non-oxide ceramics, ceramic–ceramic composites, diamond–ceramic composites, and ceramic-based cermet are presented, and excellent agreements with the experimental measurements are shown. Compared with the experimental measurements, the developed model can effectively save the cost when applied in the material design, which could be used to predict at any targeted temperature. Furthermore, the models could be used to determine the underlying control mechanisms of the temperature dependence of the hardness of the materials.

Monoclinic-to-orthorhombic phase transition in Cu2(AsO4)(OH) olivenite at high temperature: strain and mode decomposition analyses

2018 ◽  
Vol 82 (2) ◽  
pp. 347-365 ◽  
Author(s):  
Serena C. Tarantino ◽  
Michele Zema ◽  
Athos M. Callegari ◽  
Massimo Boiocchi ◽  
Michael A. Carpenter
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Single Crystal ◽  
Volume Expansion ◽  
Monoclinic Phase ◽  
Orthorhombic Phase ◽  
Unit Cell ◽  
The Other ◽  
Unit Cell Parameters ◽  
Cell Parameters

ABSTRACTA natural olivenite single crystal was submitted to in situ high-temperature single-crystal X-ray diffraction from room temperature (RT) to 500°C. Unit-cell parameters were measured at regular intervals of 25°C, and complete datasets collected at T = 25, 50, 100, 150, 200, 250, 300, 400 and 500°C. Evolution of unit-cell parameters and structure refinements indicates that olivenite undergoes a structural phase transition from P21/n to Pnnm at ~200°C, and eventually becomes isostructural with the other members of the olivenite-mineral group. Volume expansion with temperature is larger in the monoclinic phase – where it follows a non-linear trend – than in the orthorhombic one. Axial and volume expansion coefficients of the orthorhombic olivenite phase are positive and linear and similar to those of the other Cu-bearing member of the mineral family, namely libethenite, but rather different from those of the Zn-analogue arsenate adamite.Distortion of Cu polyhedra is quite high in the olivenite monoclinic phase at RT and goes towards a relative regularization with increasing T until the phase transition occurs. In the orthorhombic phase, no significant variation of the polyhedral distortion parameters is observed with increasing temperature, and maximum expansion is along the b direction and governed by corner-sharing. Landau potential provides a good representation of the macroscopic changes associated with the phase transition, coupling between the strains and the order parameter is responsible for the nearly tricritical character of the transition.

scholarly journals A Review on the High Temperature Strengthening Mechanisms of High Entropy Superalloys (HESA)

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5835
Author(s):  
Malefane Joele ◽  
Wallace Rwisayi Matizamhuka
Keyword(s):  
High Temperature ◽  
Configurational Entropy ◽  
Extended Period ◽  
Theoretical Models ◽  
Intermetallic Phases ◽  
Processing Route ◽  
Strengthening Mechanisms ◽  
High Entropy ◽  
Use Of Resources ◽  
The Impact

The studies following HEA inceptions were apparently motivated to search for single-phase solid solution over intermetallic phases, accordingly made possible by the concept of high configurational entropy. However, it was realised that the formation of intermetallic phases in HEAs is prevalent due to other criterions that determine stable phases. Nonetheless, recent efforts have been directed towards attributes of microstructural combinations. In this viewpoint, the techniques used to predict microstructural features and methods of microstructural characterisation are elucidated in HESA fields. The study further analyses shortcomings regarding the design approaches of HESAs. A brief history is given into how HESAs were developed since their birth, to emphasize the evaluation techniques used to elucidate high temperature properties of HESAs, and the incentive thereof that enabled further pursuit of HESAs in the direction of optimal microstructure and composition. The theoretical models of strengthening mechanisms in HEAs are explained. The impact of processing route on the HESAs performance is analysed from previous studies. Thereafter, the future of HESAs in the market is conveyed from scientific opinion. Previous designs of HEAs/HESAs were more based on evaluation experiments, which lead to an extended period of research and considerable use of resources; currently, more effort is directed towards computational and theoretical methods to accelerate the exploration of huge HEA composition space.

Experimental Study of High Temperature Performance of Steel Suspension Bridge Wires

2019 ◽  
Author(s):  
Jumari A. Robinson ◽  
Adrian Brügger ◽  
Raimondo Betti
Keyword(s):  
Elastic Modulus ◽  
High Temperature ◽  
High Strength Steel ◽  
Cold Working ◽  
High Strength ◽  
Suspension Bridge ◽  
Theoretical Models ◽  
Test Results ◽  
Single Wire ◽  
Steel Wires

<p>The performance of suspension bridges exposed to fire hazards is severely under-studied – so much so that no experimental data exists to quantify the safety of a suspension bridge during or after a major fire event. Bridge performance and safety rely on the integrity of the main cable and its constituent high-strength steel wires. Due to the current lack of experimental high temperature data for wires, the theoretical models use properties and coefficients from data for other types of structural steel. No other structural steel undergoes the amount of cold-working that bridge wire does, and plastic strains from cold-working can be relieved at high temperature, drastically weakening the steel. As such, this work determines the elastic modulus, ultimate strength, and general thermo-mechanical profile of the high-strength steel wires in a range of elevated temperature environments. Specifically, these tests are conducted on a bundle of 61-wires (transient), and at the single wire level (steady-state) at a temperature range of approximately 20-700°C. The test results show an alarmingly high reduction in the elastic modulus and ultimate strength with increased temperature. The degradation shown by experiments is higher than predicted by current theoretical models, indicating that use of high-temperature properties of other types of steel is not sufficient. The test results also show scaling agreement between the single wire and the 61-wire bundle, implying that a full material work up at the single- wire level will accurately inform the failure characterization of the full cable.</p>

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