Search results for "polymorphism"
showing 10 items of 1968 documents
Exploring the high-pressure behavior of the three known polymorphs of BiPO4: Discovery of a new polymorph
2015
We have studied the structural behavior of bismuth phosphate under compression. We performed x-ray powder diffraction measurements up to 31.5 GPa and ab initio calculations. Experiments were carried out on different polymorphs: trigonal (phase I) and monoclinic (phases II and III). Phases I and III, at low pressure (P < 0.2-0.8 GPa), transform into phase II, which has a monazite-type structure. At room temperature, this polymorph is stable up to 31.5 GPa. Calculations support these findings and predict the occurrence of an additional transition from the monoclinic monazite-type to a tetragonal scheelite-type structure (phase IV). This transition was experimentally found after the simultaneo…
Polymorphism and the glasslike state of cyanide mixed crystals: A mesoscopic problem.
1990
The martensitic aspect of the structural phase transitions of the alkali cyanides and their solid solutions with the alkali halides is discussed. It is suggested that the polymorphism is intimately connected with the problem of mesoscopic transformation strains. At intermediate CN concentrations a competition between glasslike inhomogeneous strains, modulated strains, and ferroelastic strains is observed.
Polymorphism in a π stacked Blatter radical: structures and magnetic properties of 3-(phenyl)-1-(pyrid-2-yl)-1,4-dihydrobenzo[ e ][1,2,4]triazin-4-yl
2020
International audience; 3-(Phenyl)-1-(pyrid-2-yl)-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl (2) demonstrates the first example of polymorphism in the family of Blatter radicals. Two polymorphs, 2α and 2β, have been identified and characterized by single crystal X-ray diffractometry and magnetic susceptibility measurements to investigate their magnetism–structure correlations. Both polymorphs form one-dimensional (1D) π stacks of evenly spaced radicals with distinctly different π–π overlap modes. Within the 1D π stacks, radicals are located at evenly interplanar distances, 3.461 Å for 2α and 3.430 Å for 2β. Magnetic susceptibility studies indicate that both polymorphs exhibit antiferromagnetic …
Luminescence of polymorph crystalline and glassy SiO2, GeO2: A short review
2009
Studies of SiO 2 and GeO 2 crystals with α-quartz and rutile structures were performed during last two decades. The goal of such studies was comparison of properties with those of glassy modifications of these crystals. Luminescence of oxygen deficient centers in these glassy materials was found to resemble the luminescence of the rutile-type modification rather than α-quartz modification. In α-quartz, similar luminescence centers appear after damaging irradiation by electron beam at low temperatures (<60 K) or at ambient temperatures after gamma or neutron irradiation.
α- and β-AgVO3 polymorphs as photoluminescent materials: an example of temperature-driven synthesis
2018
Abstract Controlling the synthesis of a given polymorph of an inorganic material is a further step in the design of property and function. In this letter, we report for the first time a simple procedure to effectively control the reversible transformation between the crystalline polymorphs α-AgVO3 and β-AgVO3. Photoluminescence emission (PL) performance is analyzed; at low temperatures (up to 35 °C) when α-AgVO3 is formed the PL emission is red, while at temperatures larger than 45 °C when β-AgVO3 is obtained the color of emission PL emission goes from green to blue. The findings highlight the ability of temperature to dramatically alter the nature of phase transformation at the atomic leve…
Polyphasic taxonomy of a novel yeast isolated from antarctic environment; description of Cryptococcus victoriae sp. nov.
1999
In 1992 some samples of mosses, lichens and soils were collected from Botany Bay, Southern Victoria Land (77 degrees 01' S 162 degrees 32' E) and, as a result of a routine screening programme some yeasts were isolated. One of them, designated as strain G5, showed marked differences when compared to other antarctic yeasts. According to morphological and physiological characteristics, we were able to identify the strain G5 as a yeast belonging to the genus Cryptococcus. Some characteristics of this genus are the growth response to myo-inositol, celobiose, raffinose and D-glucuronate, no-fermentation, the absence of mycelium and pseudomycelium, asexual reproduction, Diazolium blue B test (DBB)…
Comment on "High-pressure phases of group-II difluorides: Polymorphism and superionicity"
2018
Nelson et al. [Phys. Rev. B 95, 054118 (2017)] recently have reported first-principles calculations on the behaviour of group-II difluorides (BeF$_{2}$, MgF$_{2}$, and CaF$_{2}$) under high-pressure and low- and high-temperature conditions. The calculations were based on ab initio random structure searching and the quasi-harmonic approximation (QHA). Here, we point out that, despite the of inestimable value of such calculations at high-pressure and low-temperature conditions, the high-$P$ high-$T$ phase diagram proposed by Nelson et al. for CaF$_{2}$ neither is in qualitative agreement with the results of previous ab initio molecular dynamics simulations nor with the existing corps of exper…
Non-isotopic DNA fingerprint analyses with the minisatellite probe MZ1.3
1990
RFLP analyses with minisatellite probes yield highly informative individual specific banding patterns (genetic fingerprints) (Jeffreys et al.). Because of the complexity of the pattern and marked differences in band intensities a good band resolution and high sensitivity of the probe are essential. By reason of the latter requirement to date most of the RFLP-studies are performed with radioactive probes. Although non-isotopic labels have been introduced into fingerprint analyses (Schafer et al.; Medeiros et al.) 32P-labeled probes are still superior with respect to sensitivity. Our approach to increase the specific signal intensity makes use of an amplification of the number of probe molecu…
Origin of the natural variation in the storage of dietary carotenoids in freshwater amphipod crustaceans
2020
16 pages; International audience; Carotenoids are diverse lipophilic natural pigments which are stored in variable amounts by animals. Given the multiple biological functions of carotenoids, such variation may have strong implications in evolutionary biology. Crustaceans such as Gammarus amphipods store large amounts of these pigments and inter-population variation occurs. While differences in parasite selective pressure have been proposed to explain this variation, the contribution of other factors such as genetic differences in the gammarid ability to assimilate and/or store pigments, and the environmental availability of carotenoids cannot be dismissed. This study investigates the relati…
Genetic polymorphism and taxonomic infrastructure of the Pleurotus eryngii species-complex as determined by RAPD analysis, isozyme profiles and ecomo…
2001
The Pleurotus eryngii species-complex includes populations of choice edible mushrooms, growing in the greater Mediterranean area in close association with different genera of plants of the family Apiaceae. Their distinct host-specialization served as the principal criterion for the discrimination of several taxa; however, the genetic relationships among the various P. eryngii ecotypes remain ambiguous. In the present study, 46 Pleurotus strains with a wide range of geographical origins were isolated from Eryngium spp., Ferula communis, Cachrys ferulacea, Thapsia garganica and Elaeoselinum asclepium subsp. asclepium, and were subjected to isozyme and random amplified polymorphic DNA-PCR (RAP…