Wednesday, July 17, 2019

The density and compositional analysis of titanium doped sapphire single crystal grown by the Czocharlski method

Titanium doped sapphire (Ti:Al2O3) crystal has attracted attention not only as beautiful gemstones, but also due to their applications as high power laser action. It is very important crystal for tunable solid state laser. Ti:Al2O3 crystals have been success grown using the Czocharlski method with automatic diameter control (ADC) system. The crystals were grown with different pull rates. The structure of the crystal was characterized with X-Ray Diffraction (XRD). The density of the crystal was measurement based on the Archimedes principle and the chemical composition of the crystal was confirmed by the Energy Dispersive X-ray (EDX) Spectroscopy. The XRD patterns of crystals are showed single main peak with a high intensity. Its shows that the samples are single crystal. The Ti:Al2O3 grown with different pull rate will affect the distribution of the concentration of dopant Ti3+ and densities on the sapphire crystals boules as well on the crystal growth process. The increment of the pull rate will increase the percentage distribution of Ti3+ and on the densities of the Ti:Al2O3 crystal boules. This may be attributed to the speed factor of the pull rate of the crystal that then caused changes in the heat flow in the furnace and then causes the homogeneities is changed of species distribution of atoms along crystal.



Source:IOPscience

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Tuesday, July 9, 2019

Bi-2212 and Y123 highly curved single-crystal-like objects: whiskers, bows and ring-like structures

High-temperature superconducting objects of Bi2Sr2CaCu2O8 and Y Ba2Cu3O7 highly curved in the ab-plane, such as curved/kinked whiskers, bows and ring-like structures, were obtained within a solid–liquid–solid (SLS) grass-like growth mechanism. As-grown objects are crystals with three-dimensional epitaxy similar to conventional single crystals: they can be viewed as crystal parts 'cut' from a conventional rectangular crystal. Between our curved objects and conventional crystals, whiskers or thin films there are some differences in the superconducting properties induced only by the shape factors and no new physics is observed. Some details of the growth mechanism are discussed, emphasizing curved-line formation.


Source:IOPscience

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Thursday, June 20, 2019

A thickness-mode piezoelectric micromachined ultrasound transducer annular array using a PMN–PZT single crystal

Micro-electromechanical system (MEMS) technologies were used to develop a thickness-mode piezoelectric micromachined ultrasonic transducer (Tm-pMUT) annular array utilizing a lead magnesium niobate–lead zirconate titanate (PMN–PZT) single crystal prepared by the solid-state single-crystal-growth method. Dicing is a conventional processing method for PMN–PZT single crystals, but MEMS technology can be adopted for the development of Tm-pMUT annular arrays and has various advantages, including fabrication reliability, repeatability, and a curved element shape. An inductively coupled plasma–reactive ion etching process was used to etch a brittle PMN–PZT single crystal selectively. Using this process, eight ring-shaped elements were realized in an area of 1  ×  1 cm2. The resonance frequency and effective electromechanical coupling coefficient of the Tm-pMUT annular array were 2.66 (±0.04) MHz, 3.18 (±0.03) MHz, and 30.05%, respectively, in the air. The maximum positive acoustic pressure in water, measured at a distance of 7.27 mm, was 40 kPa from the Tm-pMUT annular array driven by a 10 Vpp sine wave at 2.66 MHz without beamforming. The proposed Tm-pMUT annular array using a PMN–PZT single crystal has the potential for various applications, such as a fingerprint sensor, and for ultrasonic cell stimulation and low-intensity tissue stimulation.



Source:IOPscience

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Friday, June 14, 2019

High infrared transmittance CdS single crystal grown by physical vapor transport

Φ55 × 15 mm2 CdS bulk single crystal with high infrared transmittance was grown by physical vapor transport. The single crystal has a consistent structure from top to bottom, which was confirmed by X-ray diffraction. The (002) full-width at half-maximum of the X-ray diffraction was measured to be 60.00 arcsec, indicating a good quality of the structure. Hall mobility, specific resistivity, and carrier concentration for the top and bottom of the crystal were observed as well. Transmittance for the CdS single crystal was measured to be higher than 70% from 2.5 to 4.5 µm, making the single crystal an important candidate for infrared window materials. Furthermore, the absorption mechanism of the CdS single crystal was analyzed.




Source:IOPscience

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Wednesday, June 5, 2019

Growth, structural and mechanical studies of phthalic acid single crystals grown in two different solutions

Good quality pure Phthalic acid single crystals were grown by slow evaporation solution growth method. Phthalic acid 1(PA1) crystals were grown in Ammonium Oxalate aqueous solution. From the aqueous solution of Ammonium Bromide, Phthalic acid 2 (PA2) crystals were grown. Single crystal x-ray diffraction and Mechanical characterizations of slow evaporation grown single crystals of PA1 and PA2 were analyzed in this article. Lattice parameters, space group and crytal system were found from Single crystal x-ray diffraction analysis. Optical tranmittance study reaveal the optical perfection of the crystals. Mechanical properties such as Vicker's microhardness number, work hardening index, standard hardness values, Yield strength, fracture toughness, brittleness index and elastic Stiffness constant values were determined using Vicker's microhardness tester.





Source:IOPscience

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Tuesday, May 28, 2019

Structural and optical properties of LuVO4 single crystals

The synthesis of large single crystals with good optical quality which is a preliminary condition for the practical applications of these materials frequently is complicated. It is found that large LuVO4 single crystals with high optical quality are possible to be prepared using high temperature solution growth method. It is obtained by X-ray crystallographic analysis that the grown crystals possess centrosymmetric tetragonal structure with the point group symmetry D4h and space group I41/amd (zircon-type structure). The unit cell parameters of a = 7.0236 Å, b = 7.0236 Å, c = 6.2293 Å, volume = 307.30(3) Å3 are measured. The crystals composition as well as vanadium oxidation state were measured in order to confirm that the crystal phase is mainly LuVO4. Optical transmission and Raman Spectroscopy are further performed on LuVO4 single crystal to reveal the optical quality and structure details


Source:IOPscience

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Thursday, May 23, 2019

PVT growth of AlN single crystals with the diameter from nano- to centi-meter level

Physical vapor transport (PVT) is the most successful and widely used approach for bulk aluminum nitride (AlN) single crystals. During the process of PVT growing AlN crystals, crucible materials, the growth setup, and the growth parameters (e.g., temperature distribution, growth pressure) are crucial. This work proposes a detailed study on the PVT growth of single AlN crystals with sizes ranging from nanometers to centimeters. AlN crystals with different sizes are grown by spontaneous nucleation. Furthermore, it discusses and contrasts the growth conditions and mechanisms of AlN crystals with different sizes. The structural and optical properties of the AlN crystals are also involved.


Source:IOPscience

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Thursday, May 9, 2019

Growth of square Si single bulk crystals with large side-face widths using noncontact crucible method

The noncontact crucible method was used to prepare square Si single bulk crystals. The size of the square part of the ingots was determined by the side-face width of the four-cornered pattern that appeared on the top surface. We obtained square Si single crystals with sizes of 9.4 × 9.7 and 10.9 × 11.0 cm2 that had no fan-shaped {110} faces and had diagonal lengths of up to 91% of the crucible diameter. To obtain large square Si single bulk crystals with a large side-face width using the present method, the importance of establishing a larger low-temperature region in the Si melt while maintaining a smaller initial temperature reduction was considered.


Source:IOPscience

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Tuesday, April 30, 2019

Coefficients of sliding friction of single crystals of high explosives under different rubbing conditions

The coefficients of sliding friction of single crystals of commonly used high explosives pentaerythritol tetranitrate (PETN), cyclotrimethylene trinitramine (RDX) and beta-cyclotetramethylene tetranitramine (β-HMX) under several rubbing configurations and at a relative sliding speed of 0.22 mm s−1 were measured. The sliding configurations were (1) crystal–polished steel pairs, (2) like-crystal pairs and (3) unlike-crystal pairs. For every rubbing configuration the friction force showed oscillations, which are thought to be caused by the formation and shearing of the adhesive junctions formed at the surface of the rubbing crystals. This shearing of the adhesive junctions led to the formation of microscopic and sub-microscopic particles, which were confirmed by an environmental scanning electron microscope study. For every rubbing configuration and for relatively high normal loads pressing the rubbing crystals together, the coefficient of friction was generally in the range 0.2–0.25 and it has been concluded that the coefficient of friction is controlled by the adhesion with almost negligible contribution from the ploughing component. From a knowledge of the coefficient of friction and the uniaxial yield stress values of single crystals of RDX and β-HMX, the shear strength of these crystals were determined to be ~13.4 MPa and ~16.8 MPa, respectively.


Source:IOPscience

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Thursday, April 25, 2019

The influence of crack face electrical boundary conditions on the nonlinear behavior of ferroelectric single crystal

The nonlinear electromechanical behavior of a cracked ferroelectric single crystal subjected to pure electrical loading is investigated by a three-dimensional phase field model for different crack face electrical boundary conditions. Phase field simulations show that crack face electrical boundary conditions have significant influence on the electrical and mechanical responses of the ferroelectric single crystal to an external electric field. The coercive field for the polarization switching of a single crystal with an electrically permeable crack is about 50% larger than that for a single crystal with an electrically impermeable crack. The remanent strain and the strain variation induced by polarization switching in a single crystal with a permeable crack are larger than those with an impermeable crack. The different macroscopic nonlinear behaviors are attributed to different polarization switching processes. It is found that domain switching takes place from the surface of a single crystal with a permeable crack, while it begins from the vicinity of the crack tip when the crack is impermeable. A ferroelectric single crystal with an impermeable crack exhibits strip 90° domain switching under a negative electric field, which is consistent with experimental observation.



Source:IOPscience

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Thursday, April 18, 2019

On the optical properties of undoped and rare-earth-doped yttrium aluminium garnet single crystals

Optical absorption and photoluminescence (PL) measurements were performed on single crystals of undoped Y3Al5O12 (YAG) and a number of rare-earth-doped YAG to study the effect of dopant type and concentration, growth atmosphere, post-growth annealing and UV irradiation on the optical properties of YAG crystals. The presence of hydrogen in the growth atmosphere was found to be essential for enhancing the incorporation of Ce ions in the Ce3+ state in Ce-doped YAG (Ce : YAG). Annealing in air was shown to have no effect on the PL emission of Ce : YAG crystals. An absorption peak around 256 nm was observed in the undoped YAG and Ce : YAG crystals after air anneal at 1200 °C. Optical absorption and annealing experiments support the association of the 256 nm peak with Fe impurities and oxygen ions. UV irradiation modifies the valency of impurities and generates electronic defects leading to an increase in the optical density of YAG crystals. Optimizing the growth and annealing conditions is critical in order to develop Ce : YAG single crystals as efficient scintillators.


Source:IOPscience

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Tuesday, April 9, 2019

Float zone single crystals for testing rods, pulled under electron beam heating

The article is devoted to the description of mathematical modelling and attempts to grow silicon single crystals from a pedestal. The crystals are intended to be used for impurity composition testing in rods with a diameter of 300 mm grown with electron beam heating. The testing is being planned both by the method of FTIR spectroscopy and by functional testing of devices that might be manufactured using single crystals grown from pedestal. The article also describes the improvements of equipment, which were necessary for crystal growth attempts, and substantial difficulties that occurred in the process and hindered single crystal growth, allowing to obtain only a polycrystalline sample.


Source:IOPscience

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Wednesday, April 3, 2019

Light emission from organic single crystals operated by electrolyte doping

Light-emitting devices based on electrolytes, such as light-emitting electrochemical cells (LECs) and electric double-layer transistors (EDLTs), are solution-processable devices with a very simple structure. Therefore, it is necessary to apply this device structure into highly fluorescent organic materials for future printed applications. However, owing to compatibility problems between electrolytes and organic crystals, electrolyte-based single-crystal light-emitting devices have not yet been demonstrated. Here, we report on light-emitting devices based on organic single crystals and electrolytes. As the fluorescent materials, α,ω-bis(biphenylyl)terthiophene (BP3T) and 5,6,11,12-tetraphenylnaphthacene (rubrene) single crystals were selected. Using ionic liquids as electrolytes, we observed clear light emission from BP3T LECs and rubrene EDLTs.



Source:IOPscience

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Monday, March 25, 2019

Segmentation Effect on Inhomogeneity of [110]-Single Crystal Deformation

This work presents a detailed analysis of segmentation process in FCC single crystals with compression axis [110] and side faces( ̅110) and (001) considering effect of octahedral shear crystal-geometry and basic stress concentrators. Sequence of meso-band systems formation on side faces is determined. Macro-segmentation patterns are specified, that are common to the FCC single crystals under investigation. It is proved that rectangular shape of highly compressed crystals, elongated in direction of operating planes, is conditioned by orientation symmetry of compression axis, single crystal side faces and shears directions, which are characteristic for the given orientation. The specified patterns are characteristic only for the samples with initial height-to-width ratio equal to 2. When varying sample height relative to the initial one, segmentation patterns will also vary due to crystal geometry variations.



Source:IOPscience

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Monday, March 18, 2019

Magnetic properties and spin structure of MnO single crystal and powder

Zero field cooled (ZFC)/Field Cooled (FC) magnetization curves of a bulk MnO single crystal show a peculiar peak at low temperatures (~ 40 K) similar to the low temperature peak observed in MnO nanoparticles. In order to investigate the origin of this peak, the spin structure of a MnO single crystal has been studied and compared with a single phase powder sample using magnetometry and polarized neutron scattering. Both magnetometry and polarized neutron diffraction results confirm the antiferromagnetic (AF) phase transition at the Néel temperature TN of 118 K, in both powder and single crystal form. However, the low temperature peak in the ZFC/FC magnetization curves is not observed in single phase MnO powder. To better understand the observed behavior, ac susceptibility measurements have been employed. We conclude that the clear peak in the magnetic signal from the single crystal originates from a small amount of ferrimagnetic (FiM) Mn2O3 or Mn3O4 impurities, which is grown at the interfaces between MnO crystal twins.



Source:IOPscience

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Wednesday, March 13, 2019

Optical non-linearities by Z-scan measurements, thermal characterization of single crystal: 8-hydroxyquinolinium 3-carboxy-4-hydroxy benzene sulfonate monohydrate

Single crystals of 8-hydroxyquinolinium 3-carboxy-4-hydroxy benzene sulfonate monohydrate were grown by slow evaporation technique at room temperature by using ethanol as solvent. Single crystal X-ray diffraction study elucidated that the crystal structure of8-hydroxyquinolinium 3-carboxy-4-hydroxy benzene sulfonate monohydrate belongs to monoclinic crystal system with space group P21/n. The solid state physical parameters have been also determined for the grown crystal from the single crystal data. The cut-off wavelength and optical band gap energy of grown crystal was found to be 420 nm and 2.67 eV respectively.Thermogravimetric and differential thermal analysis reveals that the 8-hydroxyquinolinium 3-carboxy-4-hydroxy benzene sulfonate monohydrate single crystal is thermally stable up to 144˚C without any weight loss. The mechanical properties of the grown crystal were studied by Vickers microhardness technique and it is found that 8-hydroxyquinolinium 3-carboxy-4-hydroxybenzene sulfonate monohydrate belongs to hard material category. The third order nonlinear refractive index (n2), nonlinear absorption coefficient (β) and nonlinear optical susceptibility (χ3) of the grown crystal were also measured by Z-scan studies.



Source:IOPscience

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Tuesday, March 5, 2019

Single Crystal growth of mixed anion Zr(P, Se)2 superconductor and related materials

A new method to grow single crystals of PbFCl-type mixed anion AP2-x Xx (A = Zr, Hf, X = S, Se) superconductor is examined. Using a wedge-type, cubic-anvil, high-pressure apparatus, single crystals of ZrP1.25Se0.75 (A = Zr, X = Se) were grain grown from nominal composition melts under a pressure of 2.0 GPa. Obtained Plate-like single crystal with approximate edge sizes of 160 × 160 × 20 μ m3 was measured on electron probe microanalysis and X-ray diffraction indicate that the as-grown boules are a single phase ZrP1.25Se0.75. Superconducting transition temperature (T c) is 6.31 K for ZrP1.25Se0.75 single crystal. It also succeeded in single crystal growth of substitution of nonmagnetic rare earth atoms for A (A = Zr) site, T c = 6.91 K was reached in the (Zr0.50Lu0.50)PSe nominal composition. In this paper, the crystal growth of these compound are also reported.



Source:IOPscience

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Monday, February 18, 2019

The growth of 122 and 11 iron-based superconductor single crystals and the influence of doping

This review focuses on the various single crystal growth techniques applied to the new class of high temperature superconductors—iron-based layered pnictides, such as the parent compounds AFe2As2 (A = Ba, Sr, Ca) (122), hole-doped A1 − xK x Fe2As2, electron/hole-doped AFe2 − xM x As2 (M = Co, Ni, Mn, Cr), isovalently doped AFe2As2 − xP x , the chalcogenides A x Fe2 − ySe2(A = K, Rb, Cs) (122), and Fe1 − δTe1 − xSe x (11). Detailed single crystal growth methods (fluxes, Bridgman, floating zone(FZ)), the associated procedures, and their impact on crystal size and quality are presented. We also discuss the influence of doping on the structure, and the electric, magnetic, and superconducting properties of these compounds by a comparative study of different growth methods.


Source:IOPscience

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Monday, February 11, 2019

Chemical mechanical polishing and nanomechanics of semiconductor CdZnTe single crystals

Cd0.96Zn0.04Te and  Cd0.9Zn0.1Te semiconductor wafers grown by the modified vertical Bridgman method with dimensions of 10 mm × 10 mm × 2.5 mm were lapped with a 2–5 µm polygonal Al2O3 powder solution, and then chemically mechanically polished by an acid solution having nanoparticles with a diameter of around 5 nm, corresponding to the surface roughnesses Ra of 2.135 nm, 1.968 nm and 1.856 nm. The hardness and elastic modulus of,Cd0.96Zn0.04Te and  Cd0.9Zn0.1Te single crystals are 1.21 GPa, 42.5 GPa; 1.02 GPa, 44.0 GPa; and 1.19 GPa, 43.4 GPa, respectively. After nanocutting is performed by the Berkovich nanoindenter, the surface roughness Ra of the Cd0.9Zn0.1Te single crystal attains a 0.215 nm ultra-smooth surface. The hardness and elastic modulus of three kinds of CdZnTe single crystals decrease with the increase of indentation load. When the nanoindenter departs the surface of the crystals, the adherence effects are obvious for the three kinds of single crystals. This is attributed to the plastic sticking behavior of CdZnTe material at a nanoscale level. When the indentation load of the three kinds of CdZnTe single crystals is in the range of 4000–12 000 µN, the adhered CdZnTe material on the nanoindenter falls onto the surface and accumulates around the nanoindentation.



Source:IOPscience

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Friday, February 1, 2019

Crystal growth and optical characterization of an organic single crystal for frequency conversion applications

Organic nonlinear optical 2-methylquinolinium L-malate single crystals have been grown by slow evaporation solution growth technique from a mixture of 2-methylqiunoline and L-malic acid in ethanol solution at ambient temperature. Single crystal X-ray diffraction analysis reveals that grown crystal in monoclinic system with non-centrosymmetric space group P21 and the lattice parameters are a = 7.35 Ǻ, b = 26.51 Ǻ, c = 10.83 Á, α = γ = 90° β = 102.95º and V = 2057.4 Ǻ3. UV-vis spectrum indicates that the crystal is transparent (75%) in the entire visible region with a cut-off wavelength of 437 nm and optical energy band gap Eg is found to be 2.71 eV. Microhardness measurement reveals the mechanical strength of the grown crystal. The photoluminescence spectrum shows the blue emission of the crystal. Laser damage threshold studies was carried out to ascertain the suitability of grown crystal for laser applications.The relative second harmonic generation efficiency of 2-methlquinolinium L-malate crystal was found to be two times greater than that of KDP.



Source:IOPscience

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Monday, January 21, 2019

Prediction of four, six or eight ears in drawn cups of single-crystal aluminum sheets

The new single crystal criterion developed by Cazacu, Revil and Chandola (2017) was implemented in a finite-element (FE) code and applied to forming of single-crystal cups of aluminum. Drawing simulations were conducted for circular single-crystal blanks of three different orientations: {100}〈001〉, {111} and [112] using the same set of parameters for the single-crystal yield criterion. A strong influence of anisotropy (single-crystal orientation) on the earing profile is found. While for the {100}〈001〉 orientation it is predicted that four ears develop, for the {111} and [112] crystal orientations six and eight ears are predicted, respectively. The FE simulation results are consistent with experimental observations of Tucker (1961). 


Source:IOPscience

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Monday, January 14, 2019

The effect of dopants on the brittle-to-ductile transition in silicon single crystals


The brittle-to-ductile transition (BDT) in boron, antimony and arsenic doped Cz silicon crystals has been experimentally studied, respectively. The BDT temperatures in antimony and arsenic doped silicon wafers are lower than that in a non-doped wafer while the BDT temperature in a boron doped wafer is almost the same as that in the non-doped wafer. The activation energy was obtained from the strain rate dependence of the BDT temperature. It was found that the values of the activation energy in the antimony and arsenic doped wafers are lower than that in the non-doped and boron doped wafers, indicating that the dislocation velocity in the antimony and arsenic doped silicon is faster than that in the non-doped while the dislocation velocity in the boron doped is the same as that in the non-doped. The effect of increasing in dislocation velocity on the BDT temperature was calculated by two-dimensional discrete dislocation dynamics simulations, indicating that the increasing in dislocation velocity decreases the BDT temperature in silicon single crystals.



Source:IOPscience

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Wednesday, January 9, 2019

Influence of Mn doping on CuGaS2 single crystals grown by CVT method and their characterization


1 and 2 mole% of Mn doped CuGaS2 (CGS) single crystals were grown by the chemical vapour transport (CVT) technique using iodine as the transporting agent. The analysis of the single crystal x-ray diffraction data suggests that the doping of 1 and 2 mole% Mn in the CGS single crystal does not affect the tetragonal (chalcopyrite) crystal structure. The optical absorption spectrum shows that the Mn ion induces a very strong absorption band in the UV–visible–near IR regions. The values of the crystal parameter (Dq) and the Racah parameter (B) calculated from the absorption spectra show d electron delocalization in the host crystal CGS. Room temperature photoluminescence spectra of undoped CGS only exhibited a band–band emission. But 1 and 2 mole% Mn doped CGS single crystals show two distinct CGS and Mn2+ related emissions, both of which are excited via the CGS host lattice. Raman spectra of 1 and 2 mole% Mn doped CGS single crystals exhibit a high intensity peak of the A1 mode at 310 cm−1 and 300 cm−1, respectively. EDAX, optical absorption and Raman spectrum studies reveal that Mn2+ ions are substituted in the Ga3+ ions and incorporated into the CGS lattice. The magnetization of Mn doped CGS single crystals was measured as a function of the magnetic field and temperature. Paramagnetic behaviour typical of spin S = 5/2 expected for Mn2+ (d5) magnetic centres was observed in the temperature range 2 K < T < 300 K. In Mn doping, the increase in bulk conductivity of the Mn doped CGS single crystals at room temperature indicates an increase in the hole concentration.



Source:IOPscience

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