Tetragonal Crystals Research Articles

Study of Cu2CdGeSe4 monograin powders synthesized by molten salt method for photovoltaic applications

Cu2CdGeSe4 monograin powders were synthesized by molten salt method for photovoltaic applications. The effects of salt material (CdI2 and KI), synthesis temperature and time on the structural, morphological, compositional and optoelectronic properties were investigated. Phase analysis by Raman spectroscopy and X-ray diffraction methods showed that the Cu2CdGeSe4 powder crystals synthesized at 500 °C had tetragonal structure and those synthesized at 600 °C and 700 °C had orthorhombic structure. The band gap values determined from external quantum efficiency measurements were 1.27 eV for orthorhombic Cu2CdGeSe4 and 1.14 eV for tetragonal Cu2CdGeSe4 powder crystals. The monograin layer solar cell on the base of orthorhombic Cu2CdGeSe4 powder showed the best conversion efficiency of 4.21% (active area), with an open-circuit voltage of 0.46 V, a short-circuit current density of 23.3 mA/cm2 and fill factor of 39%.

Direct observation of the domain kinetics during polarization reversal of tetragonal PMN-PT crystal

Lead magnesium niobate-lead titanate (PMN-PT) solid solutions are intensively studied for the last two decades due to their outstanding piezoelectric properties. However, despite the strong interest, there is a lack of studies of domain kinetics and domain structure evolution, which are of great importance for the development of domain engineering in PMN-PT. We present the results of the domain kinetics study during polarization reversal in tetragonal PMN-PT single crystals by in situ optical visualization accompanied by analysis of the switching current. Three types of domain structure evolution have been revealed: (1) formation and growth of macroscopic a-domains, (2) formation of charged domain walls as a result of intersections of macroscopic a-domains, and (3) formation and growth of c-domains. The domain wall motion velocities were estimated. It has been shown by comparison of the switching current and optical one that the main switching current peak is related to the growth of c-domains, whereas the small one is caused by the capacitive input of the charged domain walls. The enhancement of dielectric permittivity by two orders of magnitude due to the appearance of the charged domain walls has been revealed. The difference of forward and reverse polarization reversals was attributed to the clamped switching conditions.

One-Step Acidic Hydrothermal Preparation of Dendritic Rutile TiO₂ Nanorods for Photocatalytic Performance.

Three-dimensional and dendritic rutile TiO2 nanorods were successfully fabricated on a Ti foil surface using a one-step acidic hydrothermal method. The TiO2 nanorods were characterized using X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and optical contact angle testing. The results showed that the nanorods with diameters of 100–500 nm and lengths of 100 nm to 1 μm were obtained on the Ti foil surface. The length and density of the TiO2 nanorods were perfect at the conditions of HCl concentration 0.5 mol/L, temperature 220 °C, and reaction time 12 h. The TiO2 nanorods formed parallel to the consumption of Ti and grew along the (110) direction having a tetragonal rutile crystal. The morphology of the nanorods possessed a three-dimensional structure. The contact angle of the nanorods was only 13 ± 3.1°. Meanwhile, the photocatalytic activities of the TiO2 nanorods were carried out using ultraviolet fluorescence spectrophotometry for the methyl orange detection, and the degradation was found to be about 71.00% ± 2.43%. Thus, TiO2 nanorods can be developed by a one-step acidic hydrothermal method using Ti foil simultaneously as the substrate with a TiO2 source; the TiO2 nanorods exhibited photocatalytic performance while being environment-friendly.

Structurally Strained Bimetallic PtFe Nanocatalysts Show Tunable Catalytic Selectivity in Aqueous Oxidation of Bio-Polyols to Dicarboxylic Acids

Rational control of catalytic selectivity still remains a grand challenge in the field of biomass conversion to value-added chemicals. In this paper, we used PtFe catalyst as an example to understand fundamentals for lattice strain, electronic reconfiguration, reaction kinetics and catalytic selectivity for aqueous conversion biopolyols. Structurally strained face centered tetragonal (fct) PtFe crystals were synthesized and it was confirmed that such unique PtFe nanostructures display intriguing electronic coupling effect and partial charge distribution, as revealed by surface characterization using TEM, XRD and XPS, as well as DFT calculation. Bimetallic PtFe-fct catalysts exhibit a remarkable catalytic activity (TOF: 24 312 h–1 at 65 °C and 1 MPa O2), enhanced selectivity (tartronic acid: 54%) and improved stability for aqueous phase oxidation of biopolyols, in comparison with conventional fcc morphology. Kinetic modeling further indicates that relatively lower oxidation barrier and restrained decarboxylation reaction are key for improving selectivity on PtFe-fct catalysts.

Micro-/nanodomains and their switching in a high Curie-temperature ferroelectric single crystal of Bi(Zn2/3Nb1/3)O3-PbTiO3

Domain structure plays a critical role in the functionality of ferroelectrics. In this work, the domain structure and local domain switching behaviors of a (001)C-oriented 0.38Bi(Zn2/3Nb1/3)O3-0.62PbTiO3 single crystal with high Curie temperature (~ 430 °C) and high tetragonality (c/a > 1.04, where c and a represent the lattice parameters of the tetragonal crystal), were studied by polarized light microscopy (PLM) and piezoresponse force microscopy (PFM). Local polar domains with typical sizes from several nanometers to micrometers were observed by PFM in the crystal. The local domain switching was realized by applying a voltage, indicating the ferroelectricity of the crystal. This work provides a better understanding of the micro-/nanodomain structure and related phenomena in ferroelectrics of complex perovskite structure.

Acoustic phonons in unfilled tetragonal tungsten-bronze crystals

ABSTRACT We have studied several unfilled tetragonal tungsten-bronze crystals (SBN-35, CBN-28, CBN-30, CBN-32) by differential scanning calorimetry, Brillouin spectroscopy and piezoresponse-force microscopy. The Brillouin backscattering configuration in the c-plates revealed the longitudinal acoustic phonon, which has a frequency near 50 GHz and displays softening when approaching the phase transition in all crystals. The ferroelectric domain structure and the domain size are dependent on the Sr/Ba or Ca/Ba ratios, and on the occupation rate in the channels as shown by the piezoresponse-force microscopy images. A splitting of the longitudinal acoustic phonon was found in SBN-35 in the multidomain sample, but poling of the crystal removed this splitting and just left the phonon with higher frequency.

Crystal growth, spectroscopy and first laser operation of a novel disordered tetragonal Tm:Na2La4(WO4)7 tungstate crystal

Tm3+:Na2La4(WO4)7, a disordered tetragonal scheelite-type tungstate crystal, is grown by the Czochralski method. The polarized absorption, stimulated-emission and gain cross-section spectra are determined. The maximum σSE is 1.62 × 10–20 cm2 at 1788.6 nm for σ-polarization. The Judd-Ofelt parameters for Tm3+ are Ω2 = 10.321, Ω4 = 0.183 and Ω6 = 2.122 [10–20 cm2]. The radiative lifetime of the 3F4 state is 1.63 ms. Raman spectroscopy reveals a maximum phonon energy of 923 cm−1. Laser operation under diode-pumping is achieved with both a-cut and c-cut Tm:Na2La4(WO4)7 crystals, reaching a maximum output power for the a-cut of 715 mW at ~ 1937 nm with a slope efficiency of 34%. Microchip laser operation using the c-cut crystal yields a slope efficiency of 41%. The Tm:Na2La4(WO4)7 crystal is promising for mode-locked lasers due to its broadband emission.

Single Crystal Growth and Hierarchical Ferroelectric Domain Structure of (1–x)BiFeO3-xPbTiO3 Solid Solutions

Besides outstanding multiferroic performance, BiFeO3 has recently demonstrated a potential for novel promising applications in domain wall nanoelectronics employing domain walls with different functional properties. Rarely observed in ferroelectrics, charged domain walls are of special interest for such applications as they possess enhanced electric conductivity. In this work, single crystals of the multiferroic (1–x)BiFeO3-xPbTiO3 solid solution were successfully grown using a flux method. Structural characterization by X-ray diffraction confirmed perovskite rhombohedral R3c and tetragonal P4mm phases in crystals with x ≈ 0.2 and x ≈ 0.6, respectively. The domain structure of crystals was established with the help of polarized light microscopy, scanning electron microscopy, and piezoresponse force microscopy. In tetragonal crystals, a complex hierarchical structure of 90° lamella domains is observed with the thickness of lamellae varying from dozens of nanometers to dozens of micrometers. In the rhombohe...

Study on the influence of lysozyme crystallization conditions on crystal properties in crystallizers of varied sizes when temperature is the manipulated variable

In this work, crystallization experiments were conducted in three different sizes of crystallizers (5 and 100 ml, and 1 L) to study the influence of temperature on the crystallization of lysozyme. Lysozyme solutions with concentrations of 40 and 30 g L−1 and 10% (w/w) NaCl were used. The temperature was reduced from 20 to 0 °C with various cooling rate and stirring speed. The data indicated that crystallization with cooling but without agitation or with agitation but without cooling led to low yield and inconstancy between batches, whereas that with combined cooling and agitation resulted in tetragonal crystals with high yields. Parameters, including crystallization onset, crystal morphology, crystal size distribution, concentration, supersaturation, and yield were examined by in situ and ex situ observations. The observations within small cooling rate range of 0.030–0.111 °C min−1 indicated that minor changes in cooling rate could cause significant differences in these parameters. The comparison with thermostatic experiment showed that cooling could cause the crystal sizes to be widely dispersed. While high cooling rate lead shorter crystallization onset time and higher supersaturation, thereby result in larger crystal size, higher tendency of aggregation and wider crystal size distribution, low cooling rate can pose a great challenge to the temperature control in scale-up crystallization. The work also demonstrated that the crystallization conditions obtained from 5- to 100-ml crystallizers, from which well-defined crystals with high yields were obtained, could successfully be reproduced in 1-L crystallizer.

Bioactive\u2013hybrid\u2013zirconia implant surface for enhancing osseointegration: an in vivo study

BackgroundZirconia is characterized by a hard, dense, and chemically inert surface which requires additional surface treatments in order to enhance osseointegration. The proposed hypothesis of the study was that combination of a nano-porous surface infiltrated with a bioactive material may enhance osseointegration of zirconia implants.MethodsCustom-made zirconia implants (3.7 mm × 8 mm) were designed, milled, and sintered according to manufacturer recommendations. All implants received selective infiltration etching (SIE) technique to produce a nano-porous surface. Surface porosities were either filled with nano-hydroxy apatite particle- or platelet-rich plasma while uncoated surface served as a control (n = 12, α = 0.05). New surface properties were characterized with mercury porosimetry, XRD analysis, SEM, and EDX analysis. Implants were inserted in femur head of rabbits, and histomorphometric analysis was conducted after healing time to evaluate bone–implant contact percentage (BIC%).ResultsSelective infiltration etching produced a nano-porous surface with interconnected surface porosities. Mercury porosimetry revealed a significant reduction in total porosity percent after application of the two coating materials. XRD patterns detected hexagonal crystal structure of HA superimposed on the tetragonal crystal phase of zirconia. Histomorphometric analysis indicated a significantly higher (F = 14.6, P < 0.001) BIC% around HA–bioactive–hybrid surface (79.8 ± 3%) and PRP-coated surface (71 ± 6 %) compared to the control (49 ± 8%).ConclusionsBioactive–hybrid–zirconia implant surface enhanced osseointegration of zirconia implants.

Amorphous zirconia at high pressure

AbstractWe show, by means of ab initio calculations, that amorphous zirconia progressively transforms to a high‐density amorphous phase with the application of pressure. The average coordination number of Zr and O atoms under pressure rises gradually to 8 and 4, respectively. The main building unit of the dense noncrystalline state is the eightfold‐coordinated Zr atoms (62.5%). When the coordinated modification of Zr atoms in the zirconia crystal at high pressure and temperature conditions is considered, it can be perceived that amorphous zirconia follows a transformation mechanism similar to the one observed at high temperature but different than the one detected at high pressure. The dense disordered phase is indeed found to be locally comparable with the high‐temperature tetragonal crystal. Upon decompression, some high‐pressure arrangements are persevered in the model and a transformation into another amorphous state whose structure is intermediate between uncompressed and dense amorphous phases is observed in the simulations. The high‐pressure amorphous structures are found to be semiconductors with a band gap smaller than that of the original model.

Novel insights into the degradation of β-1,3-glucans by the cellulosome of Clostridium thermocellum revealed by structure and function studies of a family 81 glycoside hydrolase

The family 81 glycoside hydrolase (GH81) from Clostridium thermocellum is a β-1,3-glucanase belonging to cellulosomal complex. The gene encoding GH81 from Clostridium thermocellum (CtLam81A) was cloned and expressed displaying a molecular mass of ~82 kDa. CtLam81A showed maximum activity against laminarin (100 U/mg), followed by curdlan (65 U/mg), at pH 7.0 and 75 °C. CtLam81A displayed Km, 2.1 ± 0.12 mg/ml and Vmax, 109 ± 1.8 U/mg, against laminarin under optimized conditions. CtLam81A activity was significantly enhanced by Ca2+ or Mg2+ ions. Melting curve analysis of CtLam81A showed an increase in melting temperature from 91 °C to 96 °C by Ca2+ or Mg2+ ions and decreased to 82 °C by EDTA, indicating that Ca2+ and Mg2+ ions may be involved in catalysis and in maintaining structural integrity. TLC and MALDI-TOF analysis of β-1,3-glucan hydrolysed products released initially, showed β-1,3-glucan-oligosaccharides degree of polymerization (DP) from DP2 to DP7, confirming an endo-mode of action. The catalytically inactive mutant CtLam81A-E515A generated by site-directed mutagenesis was co-crystallized and tetragonal crystals diffracting up to 1.4 Å resolution were obtained. CtLam81A-E515A contained 15 α-helices and 38 β-strands forming a four-domain structure viz. a β-sandwich domain I at N-terminal, an α/β-domain II, an (α/α)6 barrel domain III, and a small 5-stranded β-sandwich domain IV.

A review of EBSD: from rudimentary on line orientation measurements to high resolution elastic strain measurements over the past 30 years.

Considering that the Electron Back Scatter Diffraction technique, EBSD, features in more than 60% of the papers published in the current conference proceedings, this review concentrates on the most recent development in the last ten years, that is, High Resolution EBSD. An outline of the theory is presented and four-point bend test results are shown proving the sensitivity of the technique for measuring elastic strain is 1 part in 10000. Other examples of its use included here are strains surrounding indents in silicon, mapping the stress concentration at grain boundaries ahead of dislocation pile ups and dislocation generation at grain boundaries due to strain ahead of nano indentations. An application is presented to distinguish the c axis direction in slightly tetragonal PZT crystals and developments in obtaining absolute strain measurement as opposed to the relative strain measurement currently the norm are discussed.

Mechanical reliability, fatigue strength and survival analysis of new polycrystalline translucent zirconia ceramics for monolithic restorations.

This study characterized the mechanical properties (static and under fatigue), the crystalline microstructure (monoclinic - m, tetragonal - t and cubic - c phase contents) and the surface topography of three yttrium-stabilized zirconia (YSZ) materials with different translucent properties, before and after aging in an autoclave (low temperature degradation). Disc-shaped specimens were produced from second generation (Katana ML/HT - high-translucent) and third generations (Katana STML - super-translucent and UTML - ultra-translucent) YSZ ceramics (Kuraray Noritake Dental Inc.), following ISO 6872-2015 guidelines for biaxial flexural strength testing (final dimensions: 15 mm in diameter and 1.2 ± 0.2 mm in thickness), and then subjected to the respective tests and analyses. ML was mainly composed of tetragonal crystals, while STML and UTML presented cubic content. Aging increased the monoclinic content for ML and did not affect STML and UTML. Topographical analysis highlights different grain sizes on the ceramic surface (UTML > STML > ML) and aging had no effect on this outcome. Weibull analysis showed the highest characteristic strength for ML both before and after aging, and statistically similar Weibull moduli for all groups. ML material also obtained the highest survival rates (ML > STML > UTML) for both fatigue strength and number of cycles to failure. All fractures originated from surface defects on the tensile side. Third generation zirconia (Katana STML and UTML) are fully stabilized materials (with tetragonal and cubic crystals), being totally inert to the autoclave aging, and presented lower mechanical properties than the second-generation zirconia (Katana ML - metastable zirconia).

Lasing properties of a Yb ion in tetragonal LuPO4 and LuVO4 isomorphic crystals: A comparative study**Project supported by the National Natural Science Foundation of China (Grant No. 11574170).

A comprehensive investigation is carried out to compare the spectroscopic properties, absorption saturation behaviors and lasing properties of a Yb ion in tetragonal LuPO4 and LuVO4 isomorphic crystals. Significant distinctions are revealed in many aspects of the lasing behavior for the Yb ion doped in the two crystal hosts, and Yb:LuPO4 proves to be superior to Yb:LuVO4 since it enables efficient laser action to be much more easily achieved. With a 0.6 mm thick crystal plate of Yb:LuPO4, an output power of 3.30 W can be generated with an optical–optical conversion efficiency of 50.8%; whereas with a 2 mm long miniature crystal rod, the output power produced can reach 8.35 W with an optical–optical conversion efficiency of 46.7%.

Synthesis and structural, optical, photocatalytic, and electrochemical properties of undoped and yttrium-doped tetragonal ZrO2 nanoparticles

Template-free undoped and yttrium-doped tetragonal ZrO2 nanoparticles were successfully synthesized using a hydrothermal technique, and their structural, morphological, optical, and electrochemical properties were characterized. The photocatalytic activity for the dye degradation of the Rhodamine B (RhB) was also studied under UV light irradiation. The tetragonal crystal phase of the nanoparticles was confirmed by XRD analysis. The observed peak shift in XRD patterns confirmed the incorporation of dopant into host lattice. The Yttrium-doped ZrO2 nanoparticles showed a higher specific surface area and smaller optical band gap (191.5 m2/g and 3.66 eV) than the pristine ZrO2 nanoparticles (108.6 m2/g and 4.94 eV). The yttrium-doped ZrO2 nanoparticles exhibited greater photocatalytic activity (~98%) than the pure ZrO2 nanoparticles within 40 min, due to their high specific surface area and reduced photogenerated charge carrier recombination rate. The Nyquist plot of yttrium-doped sample exhibited lower charge transfer resistance than that of the undoped sample. The photocurrent of the doped sample (28.6 mA/cm2) was ~9 times higher than that of pristine ZrO2 sample (3.2 mA/cm2). The doped sample showed stable and higher photocurrent density up to 520 s under light illumination.

The synthetic activities of TiO2-moringa oleifera seed powder in the treatment of the wastewater of the coal mining industry

To process the coal wastewater, the combination of chemical based technology of Advanced Oxidation Process (AOP) of a strong oxidizer using TiO2 photocatalyst and biological treatment of moringa seed powder (Moringa oleifera) is used in the composite form. AOP can be used as an alternative treatment of coal wastewater which is quite economical and environmentally friendly. The XRD results of TiO2 powder and the synthesis of TiO2 - is moringa seed powder in the form of tetragonal crystals. The degradation results of the quality of the coal wastewater using TiO2 powder reached a decrease of (TSS, Fe, Mn, Zn, Hg, Cu, Co, Cr, Al and Ni) by an average of 70% and the increase of pH value of 7 at 200 minute stirring time. The decrease of the wastewater quality using the synthesis of TiO2- moringa seed powder by using sunlight and without sunlight is detected negative (-) at 200 minute stirring time.

Synthesis and characterization of highly selective and sensitive Sn/SnO2/N-doped carbon nanocomposite (Sn/SnO2@NGC) for sensing toxic NH3 gas

In the present study, a facial synthesis of Sn/SnO2 nanoparticles embedded in nitrogen doped carbon based nanocomposites has been disclosed which was used as a fast and high-performance NH3 gas sensor. The prepared nanocomposite was characterized by various analytical technique including FTIR, TGA/DTA, Raman, XRD, FESEM, TEM/HRTEM and XPS. The presence of both Sn and SnO2 nanoparticles in carbon matrix are supported by FTIR, Raman and XRD. The XRD analysis showed the tetragonal crystal phase of SnO2 nanoparticles, and the BET results revealed 148.9 m2 g−1 surface area of the nanocomposite. Furthermore, SEM image showed that Sn and SnO2 nanoparticles were well dispersed in the nitrogen doped carbon matrix. The fabricated sensor was characterized against various concentration of NH3 and the results indicated that the prepared sensor showed excellent responses at 65 °C working temperature, with 300 ppm concentration of NH3 and the sensitivity was observed 172.70. Additionally, the fabricated sensor also showed quick response and the recovery time of 60 s and 55 s, respectively. The fabricated sensor with its quick response and recovery time, good repeatability, excellent selectivity, and slight humidity effects has the potential and could be used as NH3 sensor on industrial scale.

On the photoelastic constants and the Brewster law for stressed tetragonal crystals

An exact knowledge of the mechanical and optical properties of crystals allows not only for theoretical advances, but it is also a useful tool to asses crystal quality in the technological processes of growth and production of advanced crystals like, eg, scintillators. In this paper, we study the elasto‐optic behavior of tetragonal crystals to evaluate the photoelastic constants, associated to various states of stress, in terms of the components of the piezo‐optic tensor. Moreover, we arrive at a generalization, for tetragonal crystals, of the Brewster law for optically isotropic materials.

Large field-induced strain, giant strain memory effect, and high thermal stability energy storage in (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric single crystal

(Pb,La)(Zr,Sn,Ti)O3 (PLZST) tetragonal antiferroeletric single crystals have been grown by conventional flux method. Phase structure, domain evolution, electric field-induced strain and energy storage properties of the as-grown PLZST crystals with [100] crystallographic orientation have been investigated systematically. A large electric field-induced strain up to 0.76% at 110 °C and a giant memory strain of 0.51% at 100 °C have been realized in the PLZST crystals. This field-induced strain has a nonlinear relationship with the square polarization, which simultaneously stems from the quadratic and higher order electrostrictions. Furthermore, a good thermal stability of energy storage performance with the recoverable energy variation less than 5% in a wide temperature window (105 °C) has been achieved. The combination of high strain and good thermal stability of energy storage wound make the PLZST crystals one of the most important candidates for high temperature electromechanical coupling and high reliability energy-storage devices.