The role of water in the conductivity of vanadium pentoxide xerogel films

The measurement of DC conductivity of thin films deposited from vanadium pentoxide gels between 200 and 600 K in air, oxygen and a vacuum of 5 x 10 -7 torr has revealed that reversible changes in conductivity are determined by hydration/dehydration phenomena. The removal of weakly bonded water results in a conductivity decrease from ≃ 2 S/m to ≃ 0.3 S/m at room temperature. Heat treatment between 430 and 550 K in oxygen leads to the maximally dehydrated phase in which σ ≃ 9 × 10-3 S/m at 300 K. The essentially unchanged activation energies in all of the phases suggest that hydration affects the charge carrier concentration only.Nous avons mesuré entre 200 et 600 K la conductivité à l'air libre ou sous un vide de 5 x 10-7 torr, de couches minces obtenues à partir de gels de pentoxydes de vanadium. Ces mesures ont montré que les changements réversibles de la conductivité sont liés à des phénomènes d'hydratation et de déshydratation. Le départ de l'eau faiblement absorbée entraîne, à température ambiante, une diminution de la conductivité de ≃ 2 S/m à 0,3 S/m. Un traitement thermique entre 430 et 550 K dans une atmosphère d'oxygène conduit à une phase de déshydratation maximum avec σ ≃ 9 x 10-3 S/m à 300 K. Le fait que les énergies d'activation sont similaires dans les différentes phases suggère que le processus d'hydratation entraîne seulement une modification de la concentration des porteurs de charge

AMORPHOUS VANADIUM OXIDES BY CVD : PREPARATION, ELECTRICAL AND MAGNETIC PROPERTIES

Chemical vapour deposition of VOCl3 with H2O in controlled atmosphere is a unique method in producing amorphous vanadium oxides that contain only V5+ and V4+ ions with continuously varying valence ratio /c/ between <0.02 and ≈ 1.0. The room temperature d.c. conductivity of as prepared V2O5 films ranges between 10-5 and 10-3 ohm-1m-1 and is strongly dependent on preparation conditions. Increasing the valence ratio the conductivity first increases to ≈ 10-2 ohm-lm-1, then declines to 10-4 ohm-lm-1. EPR spectra indicate that the environment of V4+ ions is not identical in films of different compositions

The effect of modified bacterial virulence to host-pathogen relationship (Phaseolus vulgaris L. Pseudomonas savastanoi pv. phaseolicola)

The Pseudomonas savastanoi pv. phaseolicola is one of the most expressive biogen stressors of the bean (Phaseolus vulgaris L.) in Hungary. The chemical and agrotechnological defence is inefficient, so breeding is the only workable way. The conventional cultivars are susceptible to PS while most of the new industrial varieties have genetic resistance to the pathogen. The genetic background of resistance is, however, a complex system in the bean. Leaf resistance is a monogenic system, but this gene is not expressed in juvenile stage of the host. The pathogen species can be divided into different races. After inoculation with virulent strains, typical symptoms appeared on the leaves. To understand the details of host-pathogen relationships, there were carried out experiments using bacterial strains with altered virulence. Six transposon mutants of the PS were tested. Our main objective was to test these modified bacterial strains on bean cultivars of known genetic background. First we analysed the symptoms, and then the correlation between the symptoms and the multiplication of mutant bacteria. Three cultivars (Cherokee, Inka and Főnix) were tested. The infection by the virulent PS isolate produced typical symptoms on the three cultivars tested. Mutant bacteria (except strain 756) did not cause any significant symptoms on the hosts. The mutant 756 induced visible symptoms on the cultivars Cherokee and Inka. On Cherokee there were small watersoaked lesions, and HR (hypersensitivity reaction) was detected on Inka, but this was restricted to some cells only (mikro HR). The rate of multiplication of the wild type strain was much higher than the multiplication of the mutants. Bacteria were detected in the cotyledons and primordial leaf, but there is not any substantial number of bacteria in leaves, except for strains 757, 1212 and 1213. The rate of multiplication of strain 756 was intermediate. These, and other experiments can help to understand the genetic background of resistance and the host-pathogen relationship in the Pseudomonas-bean pathosystem. &nbsp

The effect of modified bacterial virulence to host-pathogen relationship (Phaseolus vulgaris L. Pseudomonas savastanoi pv. phaseolicola)

The Pseudomonas savastanoi pv. phaseolicola is one of the most expressive biogen stressors of the bean (Phaseolus vulgaris L.) in Hungary. The chemical and agrotechnological defence is inefficient, so breeding is the only workable way. The conventional cultivars are susceptible to PS while most of the new industrial varieties have genetic resistance to the pathogen. The genetic background of resistance is, however, a complex system in the bean. Leaf resistance is a monogenic system, but this gene is not expressed in juvenile stage of the host. The pathogen species can be divided into different races. After inoculation with virulent strains, typical symptoms appeared on the leaves. To understand the details of host-pathogen relationships, there were carried out experiments using bacterial strains with altered virulence. Six transposon mutants of the PS were tested. Our main objective was to test these modified bacterial strains on bean cultivars of known genetic background. First we analysed the symptoms, and then the correlation between the symptoms and the multiplication of mutant bacteria. Three cultivars (Cherokee, Inka and Főnix) were tested. The infection by the virulent PS isolate produced typical symptoms on the three cultivars tested. Mutant bacteria (except strain 756) did not cause any significant symptoms on the hosts. The mutant 756 induced visible symptoms on the cultivars Cherokee and Inka. On Cherokee there were small watersoaked lesions, and HR (hypersensitivity reaction) was detected on Inka, but this was restricted to some cells only (mikro HR). The rate of multiplication of the wild type strain was much higher than the multiplication of the mutants. Bacteria were detected in the cotyledons and primordial leaf, but there is not any substantial number of bacteria in leaves, except for strains 757, 1212 and 1213. The rate of multiplication of strain 756 was intermediate. These, and other experiments can help to understand the genetic background of resistance and the host-pathogen relationship in the Pseudomonas-bean pathosystem. &nbsp