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The experimental determination of the Sternheimer antishielding factor gamma(infinity) for Ca2+ in a sold material is reported for the first time. The gamma(infinity) value was obtained by comparing the quadrupole frequency measured by 43Ca NMR with the electric field gradient calculated in a frame of the point charge approximation in the high-Tc superconducting compound, Tl0.5Pb0.5Sr2CaCu2O7. The deduced value (gamma(infinity)= -6.1+/-.9) is about one-third of that obtained from the quantum mechanical calculations, whereas in the same sample, the gamma(infinity)value for O2- deduced by the same procedure (gamma(infinity)= -13.7+/-2.0) is very close to the calculated one.

Dans cet article, on montre que l'isotope 43 du calcium est une bonne sonde RMN pour l'etude des proprietes des oxydes supraconducteurs a haute temperature. Dans l'etat normal, par la determination du deplacement de la raie, en fonction de la temperature, on accede a la variation thermique de la susceptibilite de spin. Dans l'etat supraconducteur et plus particulierement dans l'etat mixte, la largeur de raie RMN permet d'etudier la distribution d'induction magnetique due a la presence des vortex et de determiner λ, la longueur de penetration.

The structure of sol–gel synthesized titanium oxo-polymers has been investigated using solid and liquid state 17O NMR and small angle X-ray scattering (SAXS). The growth of the titanium oxo-polymers has been controlled to produce sols and gels by adjusting two main parameters: the hydrolysis ratio H=[H2O]/[Ti] and the inhibitor ratio p=[H+]/[Ti] or a=[ acacH ]/[ Ti ] ( acacH = acetylacetone ) . The combination of 17O NMR and SAXS techniques has allowed us to determine the structure of the oxo-polymers at a local and a semi local scale. The proposed model for the structure of these oxo-polymers is based on the condensation of sub-units with a mean composition Ti(OZ)x(OH)yO2 − (x + y)/2 (OZ=Acac+OBun) and having a gyration radius of about 20–25 A. These sub-units are made with a titanium-oxo core built with μ2-O, μ3-O, μ4-O bridges and their surface is capped by the residual ligands OZ. Increasing the hydrolysis ratio H or decreasing the inhibitor ratio (p or a), mainly results in an increase of the size and the fractal dimension of the oxo-polymers, while the size and the mean composition of titanium oxo-core constituting the sub-units are apparently not modified.

We report 17O NMR and SQUID measurements in two overdoped samples of the (Tl1−xPbx)Sr2CaCu2O7 family with Tc=65K (x=0.5) and Tc≊0K (x=0.2). The line shift 17K(T) has been measured for all three, well defined, 17O NMR lines and T1T has been studied for oxygen sites in the CuO2 planes. Our results show that contrary to underdoped High-Tc materials there is no evident connection between Tc variation on increasing doping and the magnetic properties in the normal state.

In this paper we present the study of two overdoped compounds of the (Tl1−xPbx)Sr2CaCu2O7 system by 17O NMR. From the thermal variation of the 17O linewidth the presence of localized magnetic moments has been detected, these magnetic moments being located in the conducting CuO2 planes. The comparison of the Curie constants deduced from NMR data for the overdoped sample (Tc = 65K) and for the heavily overdoped sample (Tc ≅ 0K) is discussed.