High pressure lanthanum

Rare-earth compounds lanthanum compounds Not only increase burn rate of DB propellants but also exhibit plateau or mesa combustion in the middle or high pressure range [244]. 

Schaper et al. have recently examined the effect of lanthanum additions on the behaviour of alumina.820 They have shown that lanthanum ions prevent the conversion of 7-Al203 to a-Al203, a process which they believe occurs by surface diffusion. They found also that the stability of the 7-Al203 was improved by the presence of La in steam-containing atmospheres at high pressures and temperatures.826... 

A2Pt207, similar to those reported for tin, ruthenium, titanium, and several other tetravalent ions. Trivalent ions which form cubic platinum pyrochlores range from Sc(III) at 0.87 A to Pr(III) at X.14 A. Distorted pyrochlore structures are formed by lanthanum (1.18 A) and by bismuth (1.11 A). Platinum dioxide oxidizes Sb203 to Sb2(>4 at high pressure. The infrared spectra and thermal stability of the rare earth platinates have been reported previously and will not be repeated here, except to point out the rather remarkable thermal stability of these compounds decomposition to the rare earth sesquioxide and platinum requires temperatures in excess of 1200 °C. 

Sample heating up to about 2300 K is performed by applying an electric current through a cylindrical or sheet heater around the sample. The heater may be made of graphite, platinum, or lanthanum chromite. Thermal quenching is possible by turning off the current. The sample temperature decreases below 600 K in a few seconds and to ambient temperature in a minute, since the anvils and blocks act as massive heat sinks. Whether the high-pressure phase can be recovered after... 

Lanthanum (La) is the first element of the lanthanide series. Like other light lanthanide elements. La crystallizes in the double hexagonal close-packed (dhep) phase at ambient conditions. Crystal stmeture studies under high pressure on La show that it follows the regular trivalent lanthanide stmeture... 

Ratto et al. (1969) have developed a theoretical model which explains the superconductivity of lanthanum and of a-cerium at high pressures, with increasing with pressure (cf. section 2.2 below). They postulate the presence of an inner 4f shell even for these metals such that the 4f character in La and non-magnetic a-Ce tends to inhibit superconductivity this 4f character decreases with increasing pressure. Their model gives results in line with... 

This chapter deals extensively with the experimental data on the superconductivity of the rare earth metals at high pressure. The results are discussed from a phenomenological point of view emphasizing systematics. This seems appropriate at the present stage of understanding. The analysis results in rather clear-cut conclusions for the electronic structure of cerium and lanthanum. It is hoped that they will serve as a useful guide-line for future experimental and theoretical work. We would like to summarize the following results and problems. 

Kaminska A, Kaczor P, Durygin A, Suchocki A, Grinberg M (2002) Low-temperature high-pressure spectroscopy of lanthanum lutetium gallium garnet crystals doped with Cr3 -I- and Nd3+. Phys Rev B 65 104106... 

Vaitheeswaran G, Kanchana V, Heathman S et al (2007) Elastic constants and high-pressure structural transitions in lanthanum monochalcogenides from experiment and theory. Phys Rev B75 184108... 

Leger etal. (1980,1981) have described the preparation, at high pressures, of the metallic monoxides for the elements from lanthanum to samarium and have determined their structure and conductivities. A negative PAV term in the free-energy expression makes it possible to synthesize the monoxides from a mixture of the metal and the sesquioxide under pressure. These monoxides can be maintained at normal pressures after,preparation. The monoxides through NdO are metallic, golden-yellow compounds with the Ln atom being trivalent. SmO is metallic with a valence close to... 

The final step, vaporization of calcium, does not work for metals with high vapor pressure, as the metal itself would vaporize with the calcium. Instead the oxide is reduced with metallic lanthanum, which has a very low vapor pressure. Lanthanum oxide and a melt of the actual RE metal are formed. The reduction reaction occurs in a tantalum container. The reduced RE metals e.g. samarium, are vaporized and deposit on the walls of the tantalum container. This method is used for [boiling point (°C) in parenthesis] Sm (1794), Eu (1529), Tm (1950), Yb (1196). 

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