Phosphides magnetic properties

We have emphasized here the existence of P-P bonds in the phosphorus-rich compounds. The existence of metal-metal bonds in the lower phosphides is also of interest, since this has a direct bearing on their magnetic properties. 

The majority of metal phosphides have a metal arsenide analogue which they usually resanble in properties and structure (Table 8.2). Metal phosphides, arsenides and nitrides not infrequently exhibit properties similar to those of metal carbides, silicides and germanides. Some metal phosphides are very useful semiconductors, while others shew superconduction or a variety of magnetic properties. Light-emitting diodes (LEDs) and nanostructured materials are other modem applications (Chapter 12.19). 

There are many ternary phosphides containing rare earth elanents and a number of these exhibit very varied and interesting magnetic properties. Isostructural series are formed by compounds of types MNi4P2,... 

Metal phosphides have been extensively studied for many applications, for example, corrosion-resistant materials [94], catalysts for hydrodesulfurisation and hydrodenitrogenation of petroleum fuels [95-100] and oxygen barriers in capacitors [101]. In addition, applications associated with the magnetic properties of these compounds have been also studied in depth [102-105]. 

Compounds with Sc, Y, lanthanoids and actinoids are of three types. Those with composition ME have the (6-coordinated) NaCl structure, whereas M3E4 (and sometimes M4E3) adopt the body-centred thorium phosphide structure (Th3P4) with 8-coordinated M, and ME2 are like ThAsi in which each Th has 9 As neighbours. Most of these compounds are metallic and those of uranium are magnetically ordered. Full details of the structures and properties of the several hundred other transition metal-Group 15 element compounds fall outside the scope of this treatment, but three particularly important structure types should be mentioned because of their widespread occurrence and relation to other structure types, namely C0AS3,... 

Although this theory explains theoretically the experimental observations in the case of ReOj, TiO, and VO, it fails to verify the conductivity characteristics of transition metal oxides such as TiO, VO, MnO, and NiO. Band theory explains the metallic characteristics but fails to account for the electrical properties of insulators or semiconductors and metal-nonmetal transitions because of neglect of electronic correlation inherent in the one-electron approach to the problem. Although there is no universal model for description of the conductivity, magnetic and optical properties of a wide range of materials (e.g., simple and complex oxides, sulfides, phosphides), several models have been proposed (for details, see Refs. 447-453). Of these, a generally accepted one is that described by Goodenough (451). 

---