Lattice Impurity Research Articles

Preparation of High-Purity Quartz Sand by Vein Quartz Purification and Characteristics: A Case Study of Pakistan Vein Quartz

This study focuses on the purification and evaluation of the high-purity quartz (HPQ) potential of vein quartz ore from Pakistan. Vein quartz is grayish-white and translucent, with its mineral composition mainly comprising quartz crystal. Processed quartz sand is obtained from quartz raw ore through purifying technologies, including crushing, ultrasonic desliming, flotation, high-temperature calcination, water quenching, hot pressure acid leaching, and chlorination roasting. The microscopic characteristics show that the vein quartz raw ore has a medium-coarse granular metacrystalline structure, high quartz content, with only a small quantity of fine-grained K-feldspar. The inclusions primarily consist of large-sized primary inclusions and secondary fluid inclusions developed along the micro-fractures, and the content of inclusions in most areas of the crystal is very low or even nonexistent. The quartz ore with such inclusion characteristics is considered a relatively good raw material for quartz. Component analysis shows that the main impurity elements in the quartz ore are Al, K, Ca, Na, Ti, Fe, and Li, with a total impurity element content of 128.86 µg·g−1. After purification, only lattice impurity elements Al, Ti, and Li remain in the processed quartz sand, resulting in a total impurity element content of 24.23 µg·g−1, an impurity removal rate of 81.20%, and the purity of SiO2 reaching 99.998 wt.%. It is suggested that when the quartz raw ore contains high content of lattice impurity elements, such as Al, Li, and Ti, it is difficult to remove them by the current purification method. In industrial production, considering the economic cost, if quartz sand still contains high content of lattice impurity elements Al, Ti, and Li after flotation, it cannot be used as a raw material for high-end HPQ.

Limiting the lattice oxygen impurities to obtain high thermal conductivity aluminum nitride ceramics

Currently, the lattice oxygen is the key factor affecting the thermal conductivity of AlN ceramics. In this paper, three methods are proposed to limit lattice oxygen, namely reducing the original powder oxygen content, changing the debinding atmosphere, and extending the sintering time. The results show that the low powder oxygen content and protective debinding atmosphere alter the carbon and oxygen content, and further promote the formation of the Y4Al2O9 (YAM) phase. The generated YAM phase can effectively reduce the lattice oxygen in terms of thermodynamics. Prolonged high temperatures can provide kinetic conditions to reduce the lattice oxygen to 0.0343 wt%. In addition, morphological changes of the phase at the grain edges and their influence on the mechanical properties were noted. Finally, AlN ceramics with a thermal conductivity of 220 W m−1 K−1 and a flexural strength of 340 MPa were obtained. This study can provide a valuable reference for the industrial production of AlN ceramics.

Raman peak shift and broadening in crystalline nanoparticles with lattice impurities

The effect of point-like lattice impurities on nanoparticle Raman spectra is studied using both numerical and analytical methods. Particular cases of replacement atoms of various masses, vacancies, and disorder in interatomic bonds are considered. It is shown that the disorder leads not only to the broadening of optical phonon lines but also to the shift of the corresponding Raman peak. The latter can be either positive (i.e., blueshift) or negative (redshift) depending on the type of impurities. Thus there is an additional contribution to the well-known redshift that occurs due to the size-quantization (confinement) effect. Considering nanometer-sized diamond particles as a representative example, we show that the broadening and the shift are, as a rule, of the same order of magnitude. The results are discussed in the framework of the self-consistent T-matrix approach. It is argued that both effects should be considered for accurate treatment of experimental Raman spectra. Simple recipes to do so are formulated for several important cases including NV centers in nanodiamonds.

Unraveling sources of emission heterogeneity in Silicon Vacancy color centers with cryo-cathodoluminescence microscopy

Diamond color centers have proven to be versatile quantum emitters and exquisite sensors of stress, temperature, electric and magnetic fields, and biochemical processes. Among color centers, the silicon-vacancy (SiV[Formula: see text]) defect exhibits high brightness, minimal phonon coupling, narrow optical linewidths, and high degrees of photon indistinguishability. Yet the creation of reliable and scalable SiV[Formula: see text]-based color centers has been hampered by heterogeneous emission, theorized to originate from surface imperfections, crystal lattice strain, defect symmetry, or other lattice impurities. Here, we advance high-resolution cryo-electron microscopy combined with cathodoluminescence spectroscopy and 4D scanning transmission electron microscopy (STEM) to elucidate the structural sources of heterogeneity in SiV[Formula: see text] emission from nanodiamond with sub-nanometer-scale resolution. Our diamond nanoparticles are grown directly on TEM membranes from molecular-level seedings, representing the natural formation conditions of color centers in diamond. We show that individual subcrystallites within a single nanodiamond exhibit distinct zero-phonon line (ZPL) energies and differences in brightness that can vary by 0.1 meV in energy and over 70% in brightness. These changes are correlated with the atomic-scale lattice structure. We find that ZPL blue-shifts result from tensile strain, while ZPL red shifts are due to compressive strain. We also find that distinct crystallites host distinct densities of SiV[Formula: see text] emitters and that grain boundaries impact SiV[Formula: see text] emission significantly. Finally, we interrogate nanodiamonds as small as 40 nm in diameter and show that these diamonds exhibit no spatial change to their ZPL energy. Our work provides a foundation for atomic-scale structure-emission correlation, e.g., of single atomic defects in a range of quantum and two-dimensional materials.

New insight into the plastic deformation mechanisms during the SiO2 phase transition process.

The removal of lattice impurities is the key to the purification of high-purity quartz (HPQ), especially for the intracell lattice impurities. Generally, the intracell lattice impurities can be migrated to the quartz surface via roasting, then removed by acid leaching. In order to reveal the phase transition of quartz during the roasting process, the evolution of structure, bond length, volume, lattice parameter and lattice stress in original, Ti4+, Al3+/Li+ and 4H+ substituted SiO2 phases were employed to investigate the mechanisms of plastic deformation based on density functional theory calculations. Results showed that the evolution of bond lengths and volumes were mainly dominated by phase transition, and the interstitial volume in high temperature SiO2 phases was higher than that in low temperature, indicating that the phase transition from α-quartz to β-cristobalite was beneficial to the migration of interstitial impurities. In addition, the phase transition from α-quartz to β-cristobalite needs to overcome the energy barriers while the phase transition from α-cristobalite to β-cristobalite needs to overcome the lattice stress. This study therefore provides an excellent theoretical basis for the plastic deformation mechanism, for the first time, beneficial to understanding the removal mechanisms of lattice impurities.

A DFT study on the effect of lattice defects on the electronic structures and floatability of spodumene

The influences of lattice vacancies and lattice impurities on the electronic structures and floatability of spodumene were studied by the density functional theory (DFT) through analysis of partial density of states (DOS), Mulliken population, differential charge density, and frontier molecular orbitals. The calculation indicated that the effect of lattice Al, Si, and Li vacancies on the DOS, Mulliken population as well as the interaction between spodumene and oleate was insignificant. Cr, Fe, and Mn impurities caused the shift of Fermi level towards lower energy and the occurrence of peaks of impurity near Fermi level. K and Na impurities contributed little to the lowest unoccupied molecular orbital (LUMO) of spodumene, while Cr, Fe, and Mn impurities had great contribution, suggesting that Cr, Fe, and Mn impurities significantly affected the interaction between spodumene and oleate. The frontier molecular orbitals analysis indicated Cr, Fe, and Mn impurities are in favor of oleate adsorption.

Research progress of coincidence Doppler broadening of positron annihilation measurement technology in materials

Positron annihilation technique is an atomic-scale characterization method used to analyze the defects and microstructure of materials, which is extremely sensitive to open volume defects. By examining the annihilation behaviour of positrons and electrons in open volume defects, local electron density and atomic structure information around the annihilation site can be obtained, such as the size and concentration of vacancies, and vacancy clusters. In recent years, positron annihilation spectroscopy has evolved into a superior tool for characterizing features of material compared with conventional methods. The coincident Doppler broadening technique provides unique advantages for examining the local electronic structure and chemical environment (elemental composition) information about defects due to its effectiveness describing high momentum electronic information. The low momentum portion of the quotient spectrum indicates the Doppler shift generated by the annihilation of valence electrons near the vacancy defect. Changes in the peak amplitudes and positions of the characteristic peaks in the high momentum region can reveal elemental information about the positron annihilation point. The physical mechanism of element segregation, the structural features of open volume defects and the interaction between interstitial atoms and vacancy defects are well investigated by using the coincidence Doppler broadening technology. In recent years, based on the development of Doppler broadening technology, the sensitivity of slow positron beam coincidence Doppler broadening technology with adjustable energy has been significantly enhanced at a certain depth. It is notable that slow positron beam techniques can offer surface, defect, and interface microstructural information as a function of material depth. It compensates for the fact that the traditional coincidence Doppler broadening technique can only determine the overall defect information. Positron annihilation technology has been applied to the fields of second phase evolution in irradiated materials, hydrogen/helium effect, and free volume in thin films, as a result of the continuous development of slow positron beam and the improvement of various experimental test methods based on slow positron beam. In this paper, the basic principles of the coincidence Doppler broadening technique are briefly discussed, and the application research progress of the coincidence Doppler broadening technique in various materials is reviewed by combining the reported developments: 1) the evolution behaviour of nanoscale precipitation in alloys; 2) the interaction between lattice vacancies and impurity atoms in semiconductors; 3) the changes of oxygen vacancy and metal cation concentration in oxide material. In addition, coincident Doppler broadening technology has been steadily used to estimate and quantify the sizes, quantities, and distributions of free volume holes in polymers.

Impurity retention and pharmaceutical solid solutions: visualizing the effect of impurities on dissolution and growth using dyed crystals

Anisotropic incorporation of lattice impurities in acetaminophen crystals leads to anisotropic dissolution behaviors, increased drug solubility, and increased crystal fragility.

Recent advances in the marketing, impurity characterization and purification of quartz

Due to its stable physical and chemical properties and its abundance in nature, quartz is widely employed in industrial and high-tech applications. However, the presence of diverse types and states of impurities in quartz ores from different geological formations poses a challenge in the process of purifying high-purity quartz, leading to wastage of raw materials and escalated costs. This study presents the socio-economic applications of quartz, scrutinizes the formation and separation mechanisms of impurities in quartz ores from a mineralogical perspective, examines the obstacles faced in quartz purification, explains the current state of development, and provides a technical summary of quartz purification. The analysis reveals that lattice impurity elements and various types of inclusion impurities are the principal factors affecting the purity of quartz. Various green separation techniques are applied based on the composition of the quartz minerals and the state of the impurities. Standard practices may involve physical pre-treatment such as scrubbing, ultrasonic crushing, and electromagnetic pulse cracking, followed by rough cleaning through color separation, superconducting high gradient magnetic separation, and flotation, and chemical pre-treatment (high-temperature or microwave roasting with chloride doping, and ammonium sulfate thermal crushing combined with water quenching to remove gas-liquid inclusions from quartz minerals). Finally, finishing processes such as fluorine-free and catalytic hot-pressure acid leaching or microbiological purification treatment with filamentous or Aspergillus fungi are used to obtain high-purity silica sand with an anticipated purity of about 99.99%.

Migration Mechanisms of Al3+/Li+ Lattice Impurities during Phase Transition from α-Quartz to β-Quartz: An Implication for Purification of High-Purity Quartz

The quality of high-purity quartz (HPQ) that used in strategic industries is normally limited due to lattice impurities. In order to reveal the migration pathway of lattice impurities in quartz particles during phase transition from α-quartz to β-quartz, α-quartz and Al3+/Li+-substituted α-quartz (S-α-quartz) was investigated under 846.15 K and 101.325 kPa based on density functional theory. Results showed that β-quartz exhibited more interstitial volume, dominating the migration of lattice impurities. This further indicates that the phase transition process was beneficial for the migration of lattice impurity from a structural point of view. Moreover, Al3+ and Li+ mainly migrated from the intracell to lattice surface along the c axis. In addition, Li+ migrated more easily than Al3+ due to higher mean square displacement values. From a thermodynamic point of view, the lower energy barrier in the case of the Al3+ and Li+ lattice suggested that the presence of lattice impurities promoted phase transition. This study therefore provides an excellent theoretical basis for the removal of lattice impurities of HPQ from an atomic perspective, for the first time.

A Review on Removal of Iron Impurities from Quartz Mineral

Iron is one of the most stubborn impurities in quartz minerals, and the iron content partly determines the various applications of quartz. Iron can exist in quartz in the forms of iron minerals, fluid inclusions, and lattice impurities. The removal of iron and the consequent purification of quartz minerals are the key processes to obtaining high-quality quartz. Iron removal methods including conventional pre-treatment, magnetic separation, acid leaching, microbiological, roasting, and flotation, as well as combined iron removal methods in quartz ore, are herein summarized. The separation mechanism of quartz and iron impurities and the latest research progress were explained and summarized, and the development prospects of quartz purification in the future were proposed based on the current progress and limitations of quartz iron removal.

Innovative technology for preparation of high-purity silica from vein quartz ore through S-HGMS coupling acid leaching process

In the present work, an S-HGMS coupling acid leaching technology was established to prepare high-purity silica using vein quartz ore. Firstly, the magnetic properties of different phases in vein quartz were investigated through density functional theory (DFT) calculations and arranged the phases in terms of magnetic susceptibility: FeP2 > Al2SiO5 > SiO2 > Ca(Al2Si2)O8 > AlPO4. Those differences in magnetic susceptibility resulted from the spin state of electrons in the ions. After treatment using the S-HGMS process, weakly magnetic particles are effectively separated from silica particles, and the obtained silica concentrate contained SiO2 of 99.690% purity. Subsequently, lattice impurity ions were removed through a fluorine-free and low-fluoric acid leaching process. Under optimal conditions, the SiO2 purity in high-purity silica reached 99.954% and 99.990% in the two processes. The lattice parameters and volume of ɑ-quartz in high-purity silica obtained with low-fluoric acid leaching were less than those obtained with fluorine-free acid leaching. This difference can be attributed to the reaction between HF molecules and lattice impurity ions, resulting in the generation of coordination compounds. Meanwhile, HF dissolved SiO2 and opened the lattice impurity ions channel, promoting lattice impurity ions depth removal. This study established a complete set of critical technologies for preparing high-purity silica from vein quartz through the S-HGMS coupling acid leaching process, providing theoretical and scientific bases for industrial applications.

Finite temperature effects on the structural stability of Si-doped HfO2 using first-principles calculations

The structural stabilities of the monoclinic and tetragonal phases of Si-doped HfO2 at finite temperatures were analyzed using a computational scheme to assess the effects of impurity doping. We proposed a method that the finite temperature effects, i.e., lattice vibration and impurity configuration effects, are considered. The results show that 6% Si doping stabilizes the tetragonal phase at room temperature, although a higher concentration of Si is required to stabilize the tetragonal phase at zero temperature. These data indicate that lattice vibration and impurity configuration effects are important factors determining structural stability at finite temperatures.

Near-Theoretical Thermal Conductivity Silver Nanoflakes as Reinforcements in Gap-Filling Adhesives.

The rapid development of highly integrated microelectronic devices causes urgent demands for advanced thermally conductive adhesives (TCAs) to solve the interfacial heat-transfer issue. Due to their natural 2D structure and isotropic thermal conductivity, metal nanoflakes are promising fillers blended with polymer to develop high-performance TCAs. However, achieving corresponding TCAs with thermal conductivity over 10W m-1 K-1 at filler content below 30 vol% remains challenging so far. This longstanding bottleneck is mainly attributed to the fact that most current metal nanoflakes are prepared by "bottom-up" processes (e.g., solution-based chemical synthesis) and inevitably contain lattice defects or impurities, resulting in lower intrinsic thermal conductivities, only 20-65% of the theoretical value. Here, a "top-down" strategy by splitting highly purified Ag foil with nanoscale thickness is adopted to prepare 2D Ag nanoflakes with an intrinsic thermal conductivity of 398.2W m-1 K-1 , reaching 93% of the theoretical value. After directly blending with epoxy, the resultant Ag/epoxy exhibits a thermal conductivity of 15.1W m-1 K-1 at low filler content of 18.6 vol%. Additionally, in practical microelectronic cooling performance evaluations, the interfacial heat-transfer efficiency of the Ag/epoxy achieves ≈1.4 times that of the state-of-the-art commercial TCA.

Model of DC Tunneling Conductivity via Hydrogen‐Like Impurities in Heavily Doped Compensated Semiconductors

Herein, a theoretical model is proposed for the weakly temperature‐dependent electrical conductivity of compensated crystalline semiconductors with hydrogen‐like impurities near the insulator–metal concentration phase transition (Mott transition). The model uses a simple non‐stoichiometric cubic “impurity lattice” formed by the doping and compensating impurities in crystal matrix. A shift of the c‐band bottom (v‐band top) into the bandgap due to overlap of the excited states of neighboring impurities is considered. The distribution of electron (and hole) density of states in the band of ground (unexcited) states of impurities is assumed to be Gaussian. Tunneling transitions of electrons between nearest donors in the charge states () and (), and tunneling transitions of holes between acceptors in the charge states () and () are considered. It is shown that, at low temperatures, transitions of electrons (holes) near the Fermi level in the impurity band lead to electrical conductivity that weakly depends on temperature (in the form of a characteristic plateau). The results of calculating electrical resistivity in the zero‐temperature limit for the plateau region agree with the known experimental data for moderately compensated n‐ and p‐type Ge, Dia, Si, ZnSe, GaAs, InSb, and InP crystals.

Ice Shell Structure and Composition of Ocean Worlds: Insights from Accreted Ice on Earth.

Accreted ice retains and preserves traces of the ocean from which it formed. In this work, we study two classes of accreted ice found on Earth-frazil ice, which forms through crystallization within a supercooled water column, and congelation ice, which forms through directional freezing at an existing interface-and discuss where each might be found in the ice shells of ocean worlds. We focus our study on terrestrial ice formed in low temperature gradient environments (e.g., beneath ice shelves), consistent with conditions expected at the ice-ocean interfaces of Europa and Enceladus, and we highlight the juxtaposition of compositional trends in relation to ice formed in higher temperature gradient environments (e.g., at the ocean surface). Observations from Antarctic sub-ice-shelf congelation ice and marine ice show that the purity of frazil ice can be nearly two orders of magnitude higher than congelation ice formed in the same low temperature gradient environment (∼0.1% vs. ∼10% of the ocean salinity). In addition, where congelation ice can maintain a planar ice-water interface on a microstructural scale, the efficiency of salt rejection is enhanced (∼1% of the ocean salinity) and lattice soluble impurities such as chloride are preferentially incorporated. We conclude that an ice shell that forms by gradual thickening as its interior cools would be composed of congelation ice, whereas frazil ice will accumulate where the ice shell thins on local (rifts and basal fractures) or regional (latitudinal gradients) scales through the operation of an "ice pump."

Characterization of the Lattice Transitions and Impurities in Manganese and Zinc Doped Ferrite Nanoparticles by Raman Spectroscopy and X-ray Diffraction (XRD)

Temperature-induced phase transitions and the presence of impurities to the spinel phase ferrite nanoparticles were comparatively assessed using the same annealed samples, by Raman spectroscopy (RS) and X-Ray Diffraction (XRD), in order to point out advantages and disadvantages of either method depending on the research issue at hand. RS revealed gradual phase transitions from predominantly magnetite-like below 250 °C with the possibility of tracking cation vacancies, over maghemite-like at 300–600 °C, hematite-dominated in the 700–1000 °C range, and back to a spinel phase at 1100 °C with a different arrangement of cations on A-sites than the starting sample. On the other hand, XRD on the same samples showed abrupt transition from the spinel structure to hematite between 600 and 700 °C, and back to spinel at 1100 °C, but this technique performed better at revealing other oxide phases present below the identification threshold of Raman spectroscopy. Magnetization measurements support the phase transitions assignments, showing no saturation magnetization for the samples annealed at 700–900 °C, while those annealed at 1000 and 1100 °C re-gained saturation magnetization up to 31.7 emu/g. Magnetite- and maghemite-like structures in the 100–300 °C range are more clearly distinguished by RS than XRD, due to their isostructural character (both have face-centered cubic symmetry). These analytical aspects have to be understood in order to achieve more efficient and comprehensive characterization of synthesized ferrite nanoparticles.

Quantum simulation of quantum many-body systems with ultracold two-electron atoms in an optical lattice.

Ultracold atoms in an optical lattice provide a unique approach to study quantum many-body systems, previously only possible by using condensed-matter experimental systems. This new approach, often called quantum simulation, becomes possible because of the high controllability of the system parameters and the inherent cleanness without lattice defects and impurities. In this article, we review recent developments in this rapidly growing field of ultracold atoms in an optical lattice, with special focus on quantum simulations using our newly created quantum many-body system of two-electron atoms of ytterbium. In addition, we also mention other interesting possibilities offered by this novel experimental platform, such as applications to precision measurements for studying fundamental physics and a Rydberg atom quantum computation.

Morphological, spectral and toxicological features of new composite material of titanium nanodioxide with nanosilver for use in medicine and biology

The results of this study indicate that titanium dioxide nanoparticles (nano-TiO2) possess adsorptive, photocatalytic, bactericidal, virucidal and fungicidal properties, which are used in antibacterial coating, for air and water disinfection. In parallel with studies of the physicochemical characteristics of titanium dioxide, its toxicological assessment was carried out to prevent possible harmful effects on humans and the biosphere objects, followed by an assessment of the nano-TiO2 hazard class. To enhance these useful properties of nano-TiO2, nanopowders of titanium dioxide and a composite of titanium dioxide were synthesized with a silver (nano-TiO2 /Ag) by way of chemical precipitation of metatitanic acid adding silver nitrate to the composite at 500-600°C. It was stated that the synthesized nanostructures have the following characteristics: anatase crystal structure of TiO2 (anatase, rutile, brookite – natural crystalline modifications of TiO2), the size of Ag nanoparticles is 35-40 nm, TiO2 – 13-20 nm. Nanocomposite has surface defects of the crystal lattice (oxygen vacancies, impurities, excess electrons or holes), silver nanoparticles are localized on the surface of anatase TiO2, which increases adsorptive, photocatalytic, biological and specifically antibacterial properties of the composite material nano-TiO2/Ag. According to the parameters of acute intraperitoneal toxicity, the studied nanocomposite anatase nano-TiO2/Ag was classified as a moderately dangerous substance (material). Nano-TiO2 and TiO2/Ag nanocomposites do not cause local irritation to the skin, yet have a mildly irritating effect on the mucous membrane of the eye, and are also characterized by a weak sensitization effect.

Synthesis and Characterization of α-Fe2O3 Nanoparticles Prepared by PLD at Different Laser Energies

In this paper, ferric oxide nanoparticles) Fe2O3 NPs( were synthesized directly on a quartz substrate in vacuum by pulse laser deposition technique using Nd:YAG laser at different energies (171, 201,363 mJ/pulse). The slides were then heated to 700o C for 1 hour. The structural, optical, morphological, and electrical properties were studied. The optical properties indicated that the prepared thin films have an energy gap ranging from 2.28 to 2.04 eV. The XRD results showed no lattice impurities for other iron oxide phases, confirming that all particles were transformed into the α-Fe2O3 phase during the heating process. The AFM results indicated the dependence of nanoparticles size on the laser energy. As the laser energy increased, the average grain size increased from 72.6 nm to 79.02 nm. Hall effect measurement indicated that the film was an n-type semiconductor.