Crystals

16 pages, 4835 KiB

Open AccessArticle

Pressure Effects on the Thermodynamic Properties of MgSiO₃ Akimotoite

by Chang Su, Wei Song, Guang Yang, Yonggang Liu and Qingyi Li

Crystals 2024, 14(10), 837; https://doi.org/10.3390/cryst14100837 (registering DOI) - 26 Sep 2024

The thermodynamic properties of MgSiO₃ akimotoite at high temperatures and high pressures are important for investigating the phase equilibria of the Earth’s transition zone and the upper part of the lower mantle. In this paper, we present the self-consistent unit-cell volume, elastic [...] Read more.

The thermodynamic properties of MgSiO₃ akimotoite at high temperatures and high pressures are important for investigating the phase equilibria of the Earth’s transition zone and the upper part of the lower mantle. In this paper, we present the self-consistent unit-cell volume, elastic properties, and in particular, thermodynamic properties including thermal expansion, heat capacity, entropy, and Grüneisen parameter of MgSiO₃ akimotoite at pressures up to 30 GPa and temperatures to 2000 K using an iterative numerical method and available experimental data, which are consistent with the previous studies. The results show that the determined thermal expansion, heat capacity, entropy, and Grüneisen parameter exhibit a nonlinear and negative relationship with increasing pressure. Additionally, the pressure derivatives of these thermodynamic parameters along with the temperature are also presented. Full article

(This article belongs to the Section Mineralogical Crystallography and Biomineralization)

► Show Figures

Figure 1

21 pages, 13176 KiB

Open AccessArticle

Microstructure Evolution and Mechanical Properties of TiB₂/Al–Cu–Mn–Cd Composite with the Adoption of Two-Stage Solution and Aging Treatment

by Jihao Li, Zhilei Xiang, Gaoliang Shen, Jingcun Huang, Wenchao Sun, Zian Yang, Yang Han, Leizhe Li, Meng Li and Ziyong Chen

Crystals 2024, 14(10), 836; https://doi.org/10.3390/cryst14100836 - 26 Sep 2024

Abstract

In this study, in order to obtain excellent mechanical properties in TiB₂/Al–Cu–Mn–Cd composite, an optimized heat treatment, i.e., short-time solution treatment at 535 °C for 1 h following long-time solution at 523 °C for 11 h, and aging treatment, i.e., aged [...] Read more.

In this study, in order to obtain excellent mechanical properties in TiB₂/Al–Cu–Mn–Cd composite, an optimized heat treatment, i.e., short-time solution treatment at 535 °C for 1 h following long-time solution at 523 °C for 11 h, and aging treatment, i.e., aged at 170 °C for 12 h, is proposed. In addition, this study investigated the connection between microstructure evolution and mechanical properties during heat treatment. The results show that with adoption of the optimized solution treatment, the area fraction of second and eutectic Al₂Cu phases decreased from 5.08% in the as-cast state to less than 0.36% owing to improvement of dissolution efficiency in the high-temperature short-time solution. Comparing mechanical properties of the composite in the as-cast state and in the peak-aged state, average ultimate tensile strength and yield strength increased from 211.9 MPa to 523.0 MPa and from 115.8 MPa to 451.8 MPa, respectively. However, average elongation slightly decreased from 8.78% to 8.24%. Strength contribution of the peak-aged TiB₂/Al–Cu–Mn–Cd composite was mainly ascribed to Cd-rich, θ″ and θ′ precipitates. In the peak-aged state, number density and average diameter of the plate-like θ″ and θ′ precipitates reached 4.266 × 10²¹ m³ and 64.30 nm, respectively, and severe lattice distortions occurred around the Cd-rich precipitates, providing the strongest precipitation strengthening. These findings indicate that the two-stage solution treatment successfully solved the problem of the eutectic phase at the triangular grain boundary being difficult to dissolve in a TiB₂/Al-Cu-Mn-Cd composite, and excellent mechanical properties were acquired with the optimized aging treatment. Full article

(This article belongs to the Special Issue Processing, Structure and Properties of Metal Matrix Composites)

► Show Figures

Figure 1

16 pages, 323 KiB

Open AccessArticle

Three-Dimensional and Two-Dimensional Green Tensors of Piezoelectric Quasicrystals

by Markus Lazar and Eleni Agiasofitou

Crystals 2024, 14(10), 835; https://doi.org/10.3390/cryst14100835 - 26 Sep 2024

Abstract

In this work, within the framework of the linear piezoelectricity theory of quasicrystals, the three-dimensional and two-dimensional Green tensors for arbitrary piezoelectric quasicrystals are derived. In the piezoelectricity of quasicrystals, where phonon, phason and electric fields exist, we introduce the corresponding multifields by [...] Read more.

In this work, within the framework of the linear piezoelectricity theory of quasicrystals, the three-dimensional and two-dimensional Green tensors for arbitrary piezoelectric quasicrystals are derived. In the piezoelectricity of quasicrystals, where phonon, phason and electric fields exist, we introduce the corresponding multifields by developing a hyperspace notation for piezoelectric quasicrystals. Using Fourier transform and the multifield formalism, the three-dimensional Green tensor for piezoelectric quasicrystals as well as its spatial gradient necessary for applications, are derived. The solutions for the “displacement”, “distortion” and “stress” multifields in the presence of a “force” multifield in a piezoelectric quasicrystal as well as the solution of the generalised Kelvin problem, are given. In addition, the two-dimensional Green tensors of piezoelectric quasicrystals as well as of quasicrystals, are determined. Full article

(This article belongs to the Special Issue Structures, Properties and Applications of Quasicrystals)

9 pages, 2123 KiB

Open AccessArticle

Friedel Oscillations and He-He Interactions in Mo

by Xuepeng Shen, Enzhi Liang, Qian Zhan, Wei Wang and Wentong Geng

Crystals 2024, 14(10), 834; https://doi.org/10.3390/cryst14100834 - 25 Sep 2024

Viewed by 178

Abstract

Helium ions implanted into metals can form ordered bubbles that are isomorphic to the host lattice. While long-range elastic interactions are generally believed to drive bubble superlattice formation, the interactions between individual helium solutes are not yet fully understood. Our first-principles calculations reveal [...] Read more.

Helium ions implanted into metals can form ordered bubbles that are isomorphic to the host lattice. While long-range elastic interactions are generally believed to drive bubble superlattice formation, the interactions between individual helium solutes are not yet fully understood. Our first-principles calculations reveal that in molybdenum, Friedel oscillations induced by individual helium atoms generate potential barriers and wells that influence helium pairing and clustering at short He-He distances. These repulsive and attractive interactions at high concentrations provide thermodynamic driving forces that align randomly distributed helium atoms into Mo-He superlattices. Friedel oscillations may have broad impacts on solute–solute interactions in alloys. Full article

(This article belongs to the Section Crystal Engineering)

17 pages, 21722 KiB

Open AccessArticle

Multiscale Simulation Study on the Spallation Characteristics of Ductile Metal Ta under High Strain Rate Impact

by Yuntian Wang, Yuzhu Guo, Sheng Li, Yushu Li, Min Yang and Weimei Shi

Crystals 2024, 14(10), 833; https://doi.org/10.3390/cryst14100833 - 25 Sep 2024

Viewed by 239

Abstract

This work employs a multiscale simulation framework to systematically explore the spallation behavior of ductile tantalum (Ta) subjected to high strain rate impacts. The approach integrates macroscopic simulations, utilizing both the Lagrangian mesh and Smoothed Particle Hydrodynamics (SPH) methods, with microscopic molecular dynamics [...] Read more.

This work employs a multiscale simulation framework to systematically explore the spallation behavior of ductile tantalum (Ta) subjected to high strain rate impacts. The approach integrates macroscopic simulations, utilizing both the Lagrangian mesh and Smoothed Particle Hydrodynamics (SPH) methods, with microscopic molecular dynamics (MD) simulations to dissect the dynamic failure processes of tantalum. The macroscopic simulations, validated against experimental data, demonstrate the effectiveness of the SPH method in accurately capturing the spallation process. An exponential correlation between spallation strength and tensile strain rate has been established. An in-depth analysis of the free surface velocity profile indicates that the pullback signal is associated with microvoid nucleation, where the velocity drop signifies the initiation conditions for microvoid development. Additionally, the rebound rate following the pullback signal reflects the progression of damage within the spallation region. By integrating results across macro- and microscales, this work offers comprehensive insights into the complex spallation behavior of ductile tantalum under extreme conditions, advancing the understanding of its failure mechanisms at high strain rates. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials)

► Show Figures

Figure 1

16 pages, 6665 KiB

Open AccessReview

Doped, Two-Dimensional, Semiconducting Transition Metal Dichalcogenides in Low-Concentration Regime

by Mallesh Baithi and Dinh Loc Duong

Crystals 2024, 14(10), 832; https://doi.org/10.3390/cryst14100832 - 25 Sep 2024

Viewed by 228

Abstract

Doping semiconductors is crucial for controlling their carrier concentration and enabling their application in devices such as diodes and transistors. Furthermore, incorporating magnetic dopants can induce magnetic properties in semiconductors, paving the way for spintronic devices without an external magnetic field. This review [...] Read more.

Doping semiconductors is crucial for controlling their carrier concentration and enabling their application in devices such as diodes and transistors. Furthermore, incorporating magnetic dopants can induce magnetic properties in semiconductors, paving the way for spintronic devices without an external magnetic field. This review highlights recent advances in growing doped, two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors through various methods, like chemical vapor deposition, molecular beam epitaxy, chemical vapor transport, and flux methods. It also discusses approaches for achieving n- and p-type doping in 2D TMDC semiconductors. Notably, recent progress in doping 2D TMDC semiconductors to induce ferromagnetism and the development of quantum emitters is covered. Experimental techniques for achieving uniform doping in chemical vapor deposition and chemical vapor transport methods are discussed, along with the challenges, opportunities, and potential solutions for growing uniformly doped 2D TMDC semiconductors. Full article

(This article belongs to the Section Crystal Engineering)

► Show Figures

Figure 1

12 pages, 3037 KiB

Open AccessArticle

Density Functional Theory Study of Lanthanide Monoxides under High Pressure: Pressure-Induced B1–B2 Transition

by Sergio Ferrari and Daniel Errandonea

Crystals 2024, 14(10), 831; https://doi.org/10.3390/cryst14100831 - 25 Sep 2024

Viewed by 312

Abstract

Using density functional theory, we study the influence of hydrostatic pressure on the crystal structure of lanthanide monoxides, focusing on the monoxides formed by the fifteen elements of the lanthanide series, from La to Lu. Calculations are performed using two methods for the [...] Read more.

Using density functional theory, we study the influence of hydrostatic pressure on the crystal structure of lanthanide monoxides, focusing on the monoxides formed by the fifteen elements of the lanthanide series, from La to Lu. Calculations are performed using two methods for the ambient pressure B1 (NaCl type) structure, the general gradient approximation (GGA) and the local density approximation (LDA). Through a systematic comparison with existent experimental data, we find that the first method agrees better with the experiments. In addition, considering other cubic structures previously reported for lanthanide monoxides, as B2 (CsCl type) and B3 (ZnS type), we explore the possibility of the occurrence of pressure-induced phase transitions. Based on the better accuracy of GGA to describe the B1 phase at ambient conditions, we exclusively use GGA for the high pressure study. We find, for the fifteen studied compounds, that, at ambient pressure, the B1 structure is the one with the lowest enthalpy, being therefore the most thermodynamically stable structure. We also determine that, at elevated pressures, all the studied compounds undergo a structural phase transition to the B2 phase. We finally establish the relationship between pressure and volume of the unit cell, along with the associated isothermal equation of state, determining the bulk modulus. Full article

(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Third Edition))

► Show Figures

Figure 1

19 pages, 6281 KiB

Open AccessArticle

Machine Learning to Predict Workability and Compressive Strength of Low- and High-Calcium Fly Ash–Based Geopolymers

by Andrie Harmaji, Mira Chandra Kirana and Reza Jafari

Crystals 2024, 14(10), 830; https://doi.org/10.3390/cryst14100830 - 24 Sep 2024

Viewed by 364

Abstract

The potential substitution of Portland cement–based concrete with low- and high-calcium fly ash–based geopolymers was investigated. However, predicting the workability and compressive strength of geopolymers with the desired physical and mechanical properties is a complicated process because of the variety of chemical compositions [...] Read more.

The potential substitution of Portland cement–based concrete with low- and high-calcium fly ash–based geopolymers was investigated. However, predicting the workability and compressive strength of geopolymers with the desired physical and mechanical properties is a complicated process because of the variety of chemical compositions found in aluminosilicate sources. Therefore, machine-learning techniques were used to predict the physical and mechanical properties of the geopolymers and eliminate the usual trial-and-error laboratory procedures. The experimental and predicted results of geopolymer properties using the multilayer perceptron regressor, voting regressor, and XGBoost techniques were compared. The XGBoost model outperformed the other models in terms of accuracy for predicting workability and compressive strength, producing the R² of 0.96 and 0.89, respectively. Sensitivity analysis determined that the percentage of CaO had the largest effect on geopolymer workability of 27.13%. Fly ash content had the largest effect on compressive strength of 34.44%. Our approach offers a straightforward and dependable strategy for designing and optimizing fly ash–based geopolymers. Full article

(This article belongs to the Section Mineralogical Crystallography and Biomineralization)

► Show Figures

Figure 1

16 pages, 4792 KiB

Open AccessArticle

Leaching Efficacy of Ethylenediaminetetraacetic Acid (EDTA) to Extract Rare-Earth Elements from Monazite Concentrate

by Ammar S. A. Al Sheidi, Laurence G. Dyer and Bogale Tadesse

Crystals 2024, 14(10), 829; https://doi.org/10.3390/cryst14100829 - 24 Sep 2024

Viewed by 322

Abstract

Alkaline EDTA solution has been previously identified as an effective leaching agent for solubilising rare-earth oxalates. These oxalates are the product of an oxalic acid conversion leach dissolving monazite and redepositing the salt. Pervious work suggested a significant increase in recovery was observed [...] Read more.

Alkaline EDTA solution has been previously identified as an effective leaching agent for solubilising rare-earth oxalates. These oxalates are the product of an oxalic acid conversion leach dissolving monazite and redepositing the salt. Pervious work suggested a significant increase in recovery was observed between pH 8 and 10; we have demonstrated that, in an excess of EDTA, this is not the case, and the dissolution is similar. While demonstrating that, at a nominal solid loading of 100 g/L, 0.2 M EDTA solution produced the highest dissolution, elevated solids require an equivalent increase in lixiviant concentration driven by consumption. Very-high-solution concentrations (>50 g/L dissolved TREEs) were achieved at a high solid loading, indicating both that a solution equilibrium is yet to be reached and that a build-up of oxalate in the system (estimated at ~1 M) does not impact the leach efficiency. We have also demonstrated the recycling of EDTA to use in multiple stages as well as the ability to recover oxalate from this solution. Full article

(This article belongs to the Special Issue Crystallization and Purification)

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Crystals, Volume 14, Issue 10 (October 2024) – 9 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI