Single Crystal Potassium Research Articles

Characteristics of acoustic plate waves in potassium niobate (KNbO 3) single crystal

This paper presents detailed theoretical investigation of three fundamental acoustic wave modes propagating in thin plates of single crystal potassium niobate. The wave velocity and Δv/ v, the fractional velocity change produced by electrical shorting of the surface, are calculated for all propagation directions on the surfaces of X-, Y-, and Z-cut plates. It is found that acoustic plate waves can provide extremely large values of electromechanical coupling coefficient. This property makes these waves very attractive for use in a variety of sensor and signal processing applications.

Effect of orientation on kinking in single-crystal potassium hydrophthalate deformed in compression

The effect of temperature and the rate of deformation on kinking is studied in single crystals of potassium hydrophthalate compressed along two different orientations. It is shown that the crack-formation mechanism during kinking depends on the orientation of a sample. It underscores that kinking can be regarded as a rotational deformation mode.

Characterization of laser ablated silicon thin films

Using laser ablation, we deposited silicon layers consisting of clusters and crystalline domains onto glass, quartz, aluminum, titanium, copper, single-crystal silicon and single-crystal potassium bromide substrates. The microstructure and the morphology of the films were characterized by use of optical microscopy, laser scanning microscopy, atomic force microscopy, transmission electron microscopy, micro-Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The results indicated that the deposited material was composed of microcrystalline droplets, typically 3.5μm in diameter, separated by amorphous-like regions. The droplets were composed of crystalline material at their centers and an outer halo of nanometer-size particles.

Acoustic plate waves in potassium niobate singlecrystal

The characteristics of acoustic waves propagating in thin plates of single crystal potassium niobate (KNbO3) have been theoretically investigated. It is found that acoustic plate wave modes can provide much stronger electromechanical coupling (ΔV/V = 0.51) than is possible with surface acoustic waves (ΔV/V = 0.265).

The plasticity of potassium

It has been known for a long time that the low-temperature deformation behaviour of potassium is very similar to that of the refractory b.c.c. metals. Therefore it is generally assumed that the same mechanism, namely kink-pair formation in screw dislocations, determines the deformation rate below a certain knee temperature T k. A detailed investigation of the flow-stress of high-purity potassium single crystals showed that the knee-temperature is about 80 K, in contrast to values of 25–30 K reported in the earlier work. Between 80 and 4.2 K there exist three clearly distinct deformation regimes separated by bends or ‘humps’ in the curve of flow-stress versus temperature. A similar behaviour has been observed in the refractory metals. The close correspondence of these bends in b.c.c metals of radically different electronic structure strongly indicates that they are intrinsic properies of screw dislocation motion in the b.c.c. lattice and do not have their origin in details of the interatomic potential.

Landau damping and lifting of vibrational degeneracy in metallic potassium fulleride

Raman spectra are presented for single crystal metallic potassium fulleride at low temperatures. As compared to the undoped material dramatic changes in line position (\ensuremath{\Delta}\ensuremath{\omega}\ensuremath{\ge}80 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) and linewidth (\ensuremath{\gamma}\ensuremath{\ge}60 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$), particularly for the two highest and the two lowest ${\mathit{H}}_{\mathit{g}}$ modes, were observed. The lowest frequency ${\mathit{H}}_{\mathit{g}}$ modes were found to be asymmetric but structured and could be fitted with five components which exhibit a line shift-linewidth relation. The experimental results are discussed in a model of single-particle excitation (Landau damping). Electron-phonon coupling constants ${\ensuremath{\lambda}}_{\mathit{i}}$ were determined for all eight ${\mathit{H}}_{\mathit{g}}$ modes using Allen's formula. The total for all ${\ensuremath{\lambda}}_{\mathit{i}}$ was found to be 0.9 for a density of states at the Fermi level of 12 ${\mathrm{eV}}^{\mathrm{\ensuremath{-}}1}$. \textcopyright{} 1996 The American Physical Society.

The interaction of potassium with oxygen on graphite as studied by high-resolution electron energy loss spectroscopy and thermal desorption spectroscopy

High-resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS) are employed to study the interaction between oxygen and potassium on graphite in the coverage range up to 2.5 monolayers and in the temperature range 160-800 K. Annealing gives rise to a succession of different KOx complexes, partially induced by surface segregation of intercalated potassium. A vibrational excitation at 39 meV is attributed to K2O formation, in agreement with a recent interpretation of XPS and HREELS spectra of oxidized single-crystal potassium. Two vibrational excitations at 30-31 meV and 180 meV are tentatively attributed to either KO2 or K2O2. A high-temperature complex, which is an unidentified precursor to CO2 formation/desorption, has a single electron energy loss at 27 meV.

Absence of a martensitic phase transformation (even an embryonic phase) in potassium as determined by an ultrasound study.

The temperature dependence and magnetic-field dependence of the nonlocal generation of ultrasound were measured between 1.8 and 25 K in high-quality potassium single crystals. The wave associated with the elastic constant C', which is extremely sensitive to any structural phase transformation, was studied. These electromagnetic-generation experiments clearly show that no anomalies in the elastic behavior occur, either in the bulk or within the skin depth. These measurements lend no support to the existence of a martensitic phase transformation or to the existence of an embryonic martensitic state in stress-free bulk potassium single crystals or within the skin depth of these crystals.

Plasticity of high purity potassium single crystals above 30K

Plasticity of high purity potassium single crystals above 30K

High-laser-damage-threshold potassium dihydrogen phosphate crystals

Development of solid-state laser drivers of higher operating fluence is dependent upon the damage resistance of the frequency conversion crystals. We have demonstrated the correlation between the purity of the crystal growth solution and the laser damage threshold of single-crystal potassium dihydrogen phosphate (KDP). Impurities introduced in the growth process can be atomic species, inorganic or organic compounds (dissolved or particulate), or bacteria. We have developed a purification process for KDP that minimizes contamination: initial recrystallization of bulk KDP followed by ozonation to remove oxidizable material, ultrafiltration to remove nonoxidized particles, and UV-light exposure to suppress bacterial growth. We have also developed a crystal growth method that excludes load-bearing surfaces, which are a potential source of particulate contamination, from the growth environment. The method, which incorporates continuous filtration and continuous flow of the growth solution has yielded crystals with damage thresholds of 28.6 J/cm2 at 355 nm and greater than 64 J/cm2 at 1064 nm (10-ns pulse length).

Adiabatic demagnetization cooler for infrared detector

An adiabatic demagnetization cooler with an indirectly cooled superconducting magnet was fabricated for an infrared detector. The operating temperature was designed to be 0.2 K. The temperature of the sensor, which replaced the infrared detector, was successfully maintained at 0.200–0.205 K for 7 h by active magnetic field control, using single crystal chromic potassium sulphate as a magnetic working substance. Using manganese ammonium sulphate, a temperature below 0.300 K was maintained for over 12 h, although the lowest sensor temperature was 0.237 K. Yttrium aluminium garnet doped with the magnetic impurity neodymium ion (Nd 3+) was also tested, it being a substitute for paramagnetic salts from the viewpoint of easy processing and handling. Using this garnet a temperature of 0.203 K could be obtained, though this could only be maintained for 6 min. A proposal for improvement in the garnet cooling capacity has been made.

The 77Se high-resolution NMR in the single crystals of potassium and rubidium hydrogen selenites

High-resolution 77Se NMR spectra in single crystals of potassium and rubidium hydrogen selenites have been studied using the cross-polarization method. The chemical shift tensors of selenium nuclei are determined from the angular dependences of the position of lines relative to liquid H 2SeO 4. The parameters of the tensors are typical for the HSeO − 3 configuration. The spectra are measured at different temperatures to search for the phase transitions. No phase transitions were found, confirming our previous results.

The vibronic spectrum of IrCl2‐6 in low symmetry environments

AbstractThe low temperature (7–15 K) absorption spectrum of IrCl2‐6 doped in single crystals of potassium and ethylammonium hexachloro‐Sn(IV) salts, A2SnCl6, recorded at high resolution supplies further contributions to solving the assignment problem of vibrational progressions of charge transfer and ligand field spin‐orbit states. The vibrational fine structure indicates differences in vibronic coupling compared to the cubic systems.

Electron transport in zinc telluride films

ZnTe films have been prepared by hot wall epitaxy onto glass and single-crystal potassium chloride substrates. The electron transport properties in polycrystalline and single-crystal films have been reported. The electrical resistivity decreases very slowly up to dopant concentrations 1016 at./cm3 followed by a steep fall. The drift mobility appears to be fairly constant over a wide range of dopant concentrations, while it shows rapid decline on heavy doping.

Unusual spectroscopic features in the emission and absorption spectra of single-crystal potassium tetrachloroplatinate(II) (K2[PtCl4]) caused by multiple-mode excited-state distortions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTUnusual spectroscopic features in the emission and absorption spectra of single-crystal potassium tetrachloroplatinate(II) (K2[PtCl4]) caused by multiple-mode excited-state distortionsD. M. Preston, Wolfgang. Guentner, Alfred. Lechner, Guenter. Gliemann, and Jeffrey I. ZinkCite this: J. Am. Chem. Soc. 1988, 110, 17, 5628–5633Publication Date (Print):August 1, 1988Publication History Published online1 May 2002Published inissue 1 August 1988https://doi.org/10.1021/ja00225a007RIGHTS & PERMISSIONSArticle Views157Altmetric-Citations30LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (780 KB) Get e-Alerts Get e-Alerts

Directional Compton profile studies in KCl

Compton scattering of 59.54 keV gamma -rays in single-crystal potassium chloride (KCl) along the (100) and (110) directions is reported for the first time. The measured absolute profiles and the anisotropy J100(q)-J110(q) are found to be in reasonable agreement with the LCAO result except for the small deviations. The experimental and theoretical autocorrelation functions B(Z) for the two directions are compared with each other. The experimental B-value for the (100) direction was found to be in good agreement with theory whereas some deviation was observed for the (100) direction.

Current-voltage reciprocity in the magnetoresistance of simple metals

High-field magnetoresistance measurements have been made on unoriented single crystals of potassium and polycrystalline samples of indium and aluminium in fields up to 7.5 T. The measurements show that a reversal of the applied magnetic field may be replaced by an interchange of current and potential leads on the sample, no matter what the position of the contacts and the shape of the sample. Onsager's theory of reciprocal relations in irreversible processes provides a proof of this phenomenon.

Magnetic-field and polarization dependence of the direct electromagnetic generation of ultrasound in potassium.

The magnetic-field and polarization dependence of the direct electromagnetic generation of ultrasound in single-crystal potassium was studied for various angles between the incident radio-frequency electric field and the [110] direction. The studies were done at 4.2 K for the slow shear mode for propagation in the [110] direction. A cusp in the magnetic-field dependence has been observed and the position of the cusp is strongly dependent on the direction of the applied electric field. The position of the cusp was used to determine the Hall coefficient. The results are compared with recent theoretical studies of the electromagnetic generation of ultrasound.

Elasticity and anharmonicity of potassium chloride at high temperature

High temperature elasticity of single crystal potassium chloride has been studied by the Rectangular Parallelepiped Resonance (RPR) method up to 870 K (⋍ 3.8 times the Debye temperature, ϑ). The elastic stiffness moduli, C 11 and C 44, decrease linearly with temperature while C 12 increases slightly with temperature. The RPR method is particularly suited to measurements of elasticity at high temperatures, since no glues (which decompose at high temperature) are used to connect the transducers to a specimen. As a consequence, the measured spectrum closely approximates the theoretical spectrum of a specimen freely suspended in space with no external contact. The present elasticity data permits the investigation of the thermodynamic properties of potassium chloride far above the Debye temperature when used together with the previous zero-pressure data on thermal expansivity and heat capacity. The equation of state of potassium chloride is virtually unaffected by anharmonicity, even at T/ϑ=3.8. One result is that the thermal pressure for KCl above the Debye temperature linearly increases with temperature. There is also small dependence on volume, in contrast to NaCl where there is no dependence on volume.

Helicon wave studies in potassium

New experiments are reported which investigate the field dependence and anisotropy of the Hall coefficient and magnetoresistivity in single crystals of potassium. These experiments shed light on whether the electronic ground state of potassium is a charge density wave (CDW). They comprise the first independent test of the high field structure in the orientation dependence of the magnetoresistance observed by Coulter and Datars (1980) using an induced torque experiment. At similar levels of sensitivity the authors find no evidence of open orbits in potassium. This result casts doubt on the CDW hypothesis.