SmSe

Fig. 14.4 ASmGeSe4 compounds viewed parallel to the SmCeSe4 layers. Dashed lines indicate unit cell boundaries in each case. CeSe4 tetrahedra are drawn as tetrahedral solids, and the SmSe environments are drawn using a ball-stick model. In all...

Fig. 1 b. Detailed position of tig d /-bands in the alternative configurations / and /"" d for SmS, SmSe and NdS. The/ - tig transition is taken as occurring to a tig centroid appropriate to 50% of bulk collapse. 0.5 eV from the exciting photon is on average lost to the residual/ set in the case of Sm, leading to the / -> d excitation values shown. Other symbols have meaning given in Fig. 1. (N.B. The SmSe scale is shifted by 3/4 eV.)...

The measured pressure shift 12 meV/kB for SmSe will close the/ shown in Fig. lb at a pressure of 25 kB much as observed (5). 

In spite of such limitations, ceramic techniques have been widely used for the synthesis of solid materials. Mention must be made, among others, of the use of this technique for the synthesis of rare earth mono-chalcogenides such as SmS and SmSe. The method involves heating the elements, first at lower temperatures (870-1170 K) in evacuated silica tubes the contents are then homogenized, sealed in tantalum tubes and heated to around 2300 K by passing a high current through the tube [15]. 

The entropy of SmSe(g) at 298.15 K was calculated to beS°(SmSe, g, 298.15 K) = 281.8 J K mol by Kovalevskaya, Sidorenko, Lysenko, and Fesenko [75KOV/S1D]. The entropy value is not selected because all parameters required for the calculation using statistical mechanics were estimated. 

IGOR/FES] is likely to be in error. The enthalpy of formation of SmSe(g) was ealcu-lated from the enthalpy of atomisation in [74NAG/SHI] (corrected to 298.15 K by adding 3 kJ mol , estimated by the review), the selected value of the enthalpy of formation of Se(g), and the enthalpy of formation of Sm(g) in [82WAG/EVA] yielding Af//° (SmSe, g, 298.15 K) = (112.2 + 15.6) kJ-moP. Since the accuracy of the estimated thermal data cannot be ascertained the review adopts a rounded value for the enthalpy of formation of SmSe(g) with increased error bars... 

SECM SG/TC experiments were carried out to prove that the product of the initial two-electron oxidation process diffused into the solution, where it would react homogeneously and irreversibly. For these measurements, a 10 /xm diameter Au tip UME was stationed 1 /xm above a 100 /xm diameter Au substrate electrode. With the tip held at a potential of —1.3 V versus saturated mercurous sulfate electrode (SMSE), to collect substrategenerated species by reduction, the substrate electrode was scanned through the range of potentials to effect the oxidation of borohydride. The substrate and tip electrode responses for this experiment are shown in Figure 16. The fact that a cathodic current flowed at the tip, when the substrate was at a potential where borohydride oxidation occurred, proved that the intermediate formed in the initial two-electron transfer process (presumed to be mono-borane), diffused into the solution. An upper limit of 500 s 1 was estimated for the rate constant describing the reaction of this species (with water or OH ), based on the diffusion time in the experimental configuration. This was consistent with the results of the cyclic voltammetry experiments (11). 

FIG. 16 Steady-state tip (a) and substrate (b) currents as a function of substrate potential for SG/TC measurements. A 10 /am diameter Au tip, biased at —1.3 V versus SMSE, was positioned 1 /am above a 100 /am diameter substrate electrode, which was swept through the range of potentials indicated. 

---