Palladium lattice parameters

As has been shown by the X-ray diffraction method the parent metals (i.e. Pd or Ni), the a-phase, and /3-phase all have the same type of crystal lattice, namely face centered cubic of the NaCl type. However, the /9-phase exhibits a significant expansion of the lattice in comparison with the metal itself. Extensive X-ray structural studies of the Pd-H system have been carried out by Owen and Williams (14), and on the Ni-H system by Janko (8), Majchrzak (15), and Janko and Pielaszek (16). The relevant details arc to be found in the references cited. It should be emphasized here, however, that at moderate temperatures palladium and nickel hydrides have lattices of the NaCl type with parameters respectively 3.6% and 6% larger than those of the parent metals. Within the limits of the solid solution the metal lattice expands also with increased hydrogen concentration, but the lattice parameter does not depart significantly from that of the pure metal (for palladium at least up to about 100°C). 

Synthesis of alloyed silver-palladium bimetallic nanoparticles was achieved by /-irradiation of aqueous solutions containing a mixture of Ag and Pd metal ions using different Ag/Pd ratios. The synthesis of alloys implies the simultaneous radio-induced reduction of silver and palladium ions. The nanoparticles were characterized by UV-visible spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The Ag-Pd nanoparticles display a face-centered cubic (fee) crystalline structure. The lattice parameter was measured for several Ag/Pd ratios and was found to closely follow Vegard s law, which indicates the formation of homogeneous alloys. In order to avoid the simultaneous reduction of silver and palladium ions which leads to alloyed bimetallic nanoparticles. 

In (70) Kepinski et al. have reported, on the basis of XRD diagrams as well as from the precise analysis of HREM lattice fringe spacings, a 2.1% increase in the lattice parameter of the palladium particles in Pd/CeOz catalysts after prolonged... 

This probably reflects a small decrease in ionic radius of the counterion. Higher oxidation states are also generally associated with higher frequencies this is particularly marked in the case of palladium, although much less so for platinum. For the octahedral complexes, the trends follow those of the lattice parameter and, by inference, the M-H length. 

Two ternary thulium palladium silicides have been characterized. TmPd2Si has the ordered Fe3C-type of structure with space group Pnma and lattice parameters a — 7.201(2), b = 6.927(2) and c = 5.452(2) (Moreau et al., 1982 X-ray powder data). For sample preparation, see YPd 2Si. 

Fig. 4.1 Palladium swelling due to hydrogen dissolution. Comparison between two extremes 100 surfaces of fcc-Pd (left) and 3-PdH j right). The bars represent the shortest distances between two palladium atoms corresponding to the lattice parameters. Palladium atoms (r j=120 pm) are shown as large circles, hydrogen atoms (r =53 pm) as small circles (Reprinted with permission from Gurlo and Clarke (2011). Copyright 2011 Wiley)...

The crystal structure of the compound SmPd2Ge (6) was found to be of the YPd2Si type (a = 0.7501, i = 0.6996, c = 0.5673 X-ray powder diffraction) by Jorda et al. (1983). For the experimental procedure, see LaPd2Ge under La—Pd-Ge. The starting materials were palladium 99.99 mass% germanium, specpure quality samarium 99.9 mass%. Barakatova (1994) confirmed the structure type and determined the lattice parameters a = 0.7504, b= 0.6995, c = 0.5680 from X-ray powder analysis. 

To understand the adsorption properties of palladium nanoclusters on (110) surface of rutile Ti02, we studied the optimized lattice constants a and c of bulk Ti02 in rutile phase and used these results to construct the surface slabs. To obtain the bulk lattice constants, a tetragonal lax lax Ic supercell was taken and the Brillouin zone was sampled by Monkhorst-Pack mesh of 4 x 4 x 6 k-points The calculated lattice parameters, a = 4.66 A and c = 2.98 A, agree well with the experimental values of 4.594 A and 2.959 A, respectively. The optimized short and long Ti-O bond distances from our calculations are 1.97 A and 2.00 A, respectively. 

R. Lamber, S. Wetjen, N.I. Jaeger, Size dependence of the lattice-parameter of small palladium particles. Phys. Rev. B 51(16), 10968-10971 (1995)... 

Pd alloys are preferred to pure palladium, which exhibits inadequate properties for membrane applications. Pd lattice can absorb large amounts of hydrogen with eonse-quent embrittlement of the metal. In fact, at atmospheric pressure and below 300°C, hydrogen in Pd co-exists under two hydride forms, phases a and p, with different lattice parameters, 0.3894 and 0.4025 nm, respectively. Transition between these two phases produces cyclic lattice strains that, at macroscopic level, are responsible for the embrittlement of the metal [4,14-16]. 

Correlation between the lattice parameter differences of palladium and palladium alloys and composition (room temperature). (Reprinted from Reference 18.)... 

The temperature independence of the Korringa product T T is a better indicator of the metallic character of an NMR signal than the value of its shift. In most metal hydrides, the spin lattice relaxation at room temperature contains important contributions from the diffusive motion of the proton in the hydride lattice. To investigate the Korringa product one must work at relatively low temperatures for the palladium hydrides only values of x > 0.65 are accessible (Fig. 20). For x = 1, 7 T = 46 sK (67), but no values have been given for the shift. Supposing that the total shift 5(1) can be derived from Eq. (21) with the parameters given previously for the palladium black, we obtain 5(1) 51 ppm. From the Ti T value... 

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