Anomalous mixed crystals

A number of authors investigated the effect of temperature (108.1451, agitation (131,1321, and acidity of the solution (841 on the isomorphous distribution of impurities. 

---

Solid solutions can also be formed to a limited extent with substances that have a similar formula but a different crystal structure. One of the substances imposes its structure upon the other. In lattices which are stable even if some sites in the unit cell are unoccupied, substances with different formulae can form solid solutions (anomalous mixed crystals). The incorporated ions must be of similar size, but do not need to have the same valency because electroneutrality is ensured by the presence of a compensating valency elsewhere in the lattice. Changes in the relative concentrations in the solid solutions lead to continuous variation of their properties. 

For convenience we distinguish (i) anomalous solid solutions in elements, (ii) anomalous mixed crystals of ionic solids (heterotype solid solutions) and (iii) controUed-valency semi-conductors. 

Anomalous mixed crystals of Am coprecipitate with K2SO4. 

Contrary to anomalously distant reacting double bonds, the mixed crystal of 1 1 donor-acceptor type cinnamic acids has been reported to be photostable, in which double bonds of adjacent donor and acceptor components in the stack are within photoreactive distance of each other (3.80 A) (14). 

Radionuclides that are able to form normal or anomalous mixed erystals with the macrocomponent are ineorporated at lattice sites. In most cases the distribution in the lattice is heterogeneous, i.e. the concentration of the microcomponent varies with the depth. If the solubility of the microcomponent is lower than that of the maero-eomponent, it is enriehed in the inner parts of the crystals. Heterogeneous distribution may even out over longer periods of time by diffusion or recystallization. 

This area has been widely investigated since the discovery by Zintl and Croatto (1939) of the existence of so-called anomalous or heterotype mixed crystals in the system CeOz-LazOs. These grossly non-stoichiometric phases, which often have wide compositional ranges, are virtually unique in oxide systems, and some have the important property of good anionie conduction (Mobius, 1964). However, in spite of much research effort there is still considerable disagreement on the precise nature of the phase equilibria in such systems. 

On June 11, 1965, the author (H. Hayashi) and Dr. K. Itoh visited Dr. Y. Kurita at his office in The Basic Research Laboratory of Toyo Rayon Company, Ltd. and saw his beautiful ESR spectra of radical pairs ( J and K ) in single crystals of dimethylglyoxime irradiated by X-rays at 77 K [2]. Here, the radical pairs J and K are symmetric and asymmetric pairs, respectively, as shown in Fig. 4-2. The typical ESR spectra observed for the radical pairs J and K are shown in Fig. 4-3. The author noticed from Fig. 4-3(b) that the central three lines of the nine hyperfme (HF) lines due to two nitrogen atoms of K were not equally spaced [3], but that there is no anomaly in the HF lines of J as shown in Fig. 4-3(a). We found that the anomalous HF lines of K could be explained by the mixing of the singlet and triplet states of a radical pair in the complete Spin Hamiltonian of the pair developed by Dr. Itoh [3]. This theory has been called "the radical pair mechanism". 

The peculiar temperature and composition dependence of the valence of chemically collapsed phases of SmS was first observed in the system Sm1 xGdxS (55). Recently a phase diagram in the (x, T)-plane has been proposed for this system (41) as well as for CeTh alloys (44). When cooled below about 200 K the chemically collapsed phases of SmS show a dramatic lattice expansion, in some cases with explosive character (55) and disintegration of the crystal into a black powder. An example of this transition towards a more divalent state of Sm on cooling in SmAs 18 S 82 and Sm 81 Y19S is shown in Fig. 22 and 23, where we show the data of Poliak et al (63). The temperature dependent configurational mixing of Sm ions which is directly visualized in the XPS data is the source of the anomalous temperature dependence of the lattice constant. No detailed analysis of the dependence of the Sm 4/lineshape on temperature... 

---