Single crystal

About: Single crystal is a research topic. Over the lifetime, 59617 publications have been published within this topic receiving 870828 citations.

Crystal structures of quinacridones

Abstract: The crystal structure of the αI-phase of quinacridone was determined from non-indexed X-ray powder data by means of crystal structure prediction and subsequent Rietveld refinement. This αI-phase is another polymorph than the α-phase reported by Lincke [G. Lincke and H.-U. Finzel, Cryst. Res. Technol. 1996, 31, 441–452.]. The crystal structures of the β and γ polymorphs were determined from single crystal data. The knowledge of the crystal structures can be used for crystal engineering, i.e., for targeted syntheses of pigments having desired properties, especially for the syntheses of new red pigments.

Optimum inhomogeneity of local lattice distortions in La2CuO4+y

Abstract: Electronic functionalities in materials from silicon to transition metal oxides are, to a large extent, controlled by defects and their relative arrangement. Outstanding examples are the oxides of copper, where defect order is correlated with their high superconducting transition temperatures. The oxygen defect order can be highly inhomogeneous, even in optimal superconducting samples, which raises the question of the nature of the sample regions where the order does not exist but which nonetheless form the “glue” binding the ordered regions together. Here we use scanning X-ray microdiffraction (with a beam 300 nm in diameter) to show that for La2CuO4+y, the glue regions contain incommensurate modulated local lattice distortions, whose spatial extent is most pronounced for the best superconducting samples. For an underdoped single crystal with mobile oxygen interstitials in the spacer La2O2+y layers intercalated between the CuO2 layers, the incommensurate modulated local lattice distortions form droplets anticorrelated with the ordered oxygen interstitials, and whose spatial extent is most pronounced for the best superconducting samples. In this simplest of high temperature superconductors, there are therefore not one, but two networks of ordered defects which can be tuned to achieve optimal superconductivity. For a given stoichiometry, the highest transition temperature is obtained when both the ordered oxygen and lattice defects form fractal patterns, as opposed to appearing in isolated spots. We speculate that the relationship between material complexity and superconducting transition temperature Tc is actually underpinned by a fundamental relation between Tc and the distribution of ordered defect networks supported by the materials.

High-Yield Synthesis of Single-Crystal Nanosprings of ZnO

Abstract: Zinc oxide, an important member in the II–VI group semiconductors, has profound applications in optics, optoelectronics, sensors, and actuators due to its semiconducting, piezoelectric, and pyroelectric properties. Structurally, wurtzite-structured ZnO has 13 fast growth directions: [0001], <011̄0> , and <21̄1̄0> ; 12 lower energy facets, {011̄0} and {21̄1̄0}; as well as a pair of polar surfaces, {0001}. These structural features allow ZnO to exhibit a group of unique and novel nanostructures, such as nanowires, nanotubes, nanobelts, nanocombs, nanosprings, nanorings, nanobows, nanojunction arrays, nanopropeller arrays, nanoplatelets, and nanodiskettes. The diversity and splendid nanostructures of ZnO could confer on it the same importance as that of carbon nanotubes for exploring nanoscale phenomena and devices. The single-crystal nanorings and nanosprings of ZnO, for example, are potential candidates for building semiconducting and piezoelectric resonators, actuators, and sensors for chemical and biological detection. It is necessary, as the first step, to synthesize nanosprings at high yield. However, the formation of nanosprings relies on nanobelts that are dominated by the {0001} polar surfaces, which have higher energy than the {011̄0} and {21̄1̄0} planes, and are energetically unfavorable to form during growth. An energy barrier has to be overcome by controlling growth kinetics to form polar-surface-dominated nanosprings. Therefore, the yield of nanosprings was lower than 5%, greatly limiting their application in electromechanical-coupled nanodevices. In this paper, we report the successful manipulation of growth kinetics to synthesize single-crystal ZnO nanorings at a high yield of more than 50%. This work pushes ZnO nanosprings from a scientific phenomenon to a practical material for carrying out a wide range of physical, mechanical, chemical, and biological experimental studies. The rational control of high-yield synthesis of piezoelectric ZnO nanosprings could open a new era in ZnO-based electromechanical-coupled nanodevices.