Zur Kenntnis der Zustandsdiagramme SECl3/MCl2 (SE = La,Sm, Gd,Yb; M = Sr,Ba)

On Phase Diagrams of Rare Earth Trichlorides/MCl₂ (Rare Earth = La, Sm, Gd, yb; M = Sr, Ba) The systems LaCl₃(SmCl₃, GdCl₃, YbCl₃)? SrCl₂(BaCl₂) were determined by difference thermal analysis. The phase diagrams contain compounds of the formula BaLnCl₅, M₂LnCl₇, Ba₃LnCl₉ and probably Sr₄LnCl₁₁, which decompose peritectoidally resp. peritectically. Sr₂SmCl₇ and Sr₂GdCl₇ are isotypic, and as indicated by the very similar reflection patterns of the Guinier photographs related to the structure of the compound Sm₃Cl₇. The phase diagrams are comparable to the systems LnCl₃? LnCl₂ with similar radii quotients of the cations. The enthalpies of mixing of the systems LaCl₃(GdCl₃, YbCl₃)? SrCl₂ were measured calorimetrically. The values are exothermic, the minima were found at approximately 65 mol-% SrCl₂.     

A Convenient Preparation of Malonoylperoxides

Cyclic Malonoyl peroxides, first reported in 1971 (1) are an important class of compounds for the study of α-lactones (2). These peroxides were prepared by treating a substituted malonic acid with 98% hydrogen peroxide in methanesulfonic acid. A serious disadvantage of this method is the use and the storage of concentrated hydrogen peroxide as well as the remote control device recommended (3) for the operation of this explosive reagent.     

Hysteretic spin-density-wave ordering in confined geometries

We have measured the antiferromagnetic spin-density-wave (SDW) order in Cr/Cr(97.5)Mn2.5(001) superlattices. The Mn doping creates a high Néel temperature layer that confines the incommensurate SDW order within the Cr layers. With temperature cycling we observe a transition from commensurate to incommensurate SDW order and discrete changes in the SDW period. We find that these transitions show significant hysteresis (up to 75 K) when the number of SDW nodes within the Cr layer changes by an odd number, while there is no hysteresis for changes of an even number of nodes. This results from the competition between maintaining the spin structure at the interfaces and introducing a spin slip at the nodes of the Cr SDW.     

The intermediate disorder regime for a directed polymer model on a hierarchical lattice

We study a directed polymer model defined on a hierarchical diamond lattice, where the lattice is constructed recursively through a recipe depending on a branching number $b\in \mathbb{N}$ and a segment number $s\in \mathbb{N}$. When $b\le s$ it is known that the model exhibits strong disorder for all positive values of the inverse temperature $\beta$, and thus weak disorder reigns only for $\beta =0$ (infinite temperature). Our focus is on the so-called intermediate disorder regime in which the inverse temperature $\beta \equiv {\beta }_n$ vanishes at an appropriate rate as the size $n$ of the system grows. Our analysis requires separate treatment for the cases $b<s$ and $b=s$. In the case $b<s$ we prove that when the inverse temperature is taken to be of the form ${\beta }_n=\stackrel{?}{\beta }{(b/s)}^{n/2}$ for $\stackrel{?}{\beta }>0$, the normalized partition function of the system converges weakly as $n\to \infty$ to a distribution $L\left(\stackrel{?}{\beta }\right)$ and does so universally with respect to the initial weight distribution. We prove the convergence using renormalization group type ideas rather than the standard Wiener chaos analysis. In the case $b=s$ we find a critical point in the behavior of the model when the inverse temperature is scaled as ${\beta }_n=\stackrel{?}{\beta }/n$; for an explicitly computable critical value ${\kappa }_b>0$ the variance of the normalized partition function converges to zero with large $n$ when $\stackrel{?}{\beta }\le {\kappa }_b$ and grows without bound when $\stackrel{?}{\beta }>{\kappa }_b$. Finally, we prove a central limit theorem for the normalized partition function when $\stackrel{?}{\beta }\le {\kappa }_b$.     

Synthesis of homogeneous pentenary chalcopyrite alloys with a classical two-step growth process

Homogeneous single-phase Cu(In_0.75Ga_0.25)(Se_1−yS_y)₂ chalcopyrite alloys were prepared by a novel two-step growth process. CuIn_0.75Ga_0.25 precursors were deposited by DC magnetron sputtering and the subsequent reaction processes in a reactive H₂Se/Ar/H₂S atmosphere was optimized to prevent the formation and separation of stable ternary phases. X-ray diffraction (XRD) analysis of these films revealed characteristic chalcopyrite peaks with a high degree of symmetry, indicative of homogeneous rather than compositionally graded material. The lattice parameters of the single-phase Cu(In_0.75Ga_0.25)(Se_1−yS_y)₂ pentenary alloys decreased linearly with an increase in the S/(S+Se) ratio in accordance with Vegard's law. X-ray photoelectron spectroscopy (XPS) depth profiling confirmed the in-depth compositional uniformity of the pentenary alloys, prepared under optimized selenization/sulfurization conditions.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.