Thermal expansion anomalous

Fig. 72. Linear thermal expansion of Lao 6Yo.o7Cao.33MnOj. Inset anomalous thermal expansion contribution...

These two methods of synthesis have led to the discovery that at compositions around x = 2, a monophase, polycrystalline NASION is very difficult to produce, even though it can be sintered to reasonable mass density ( >3.20 g/cm ) at relatively low temperatures (1100-1375°C). Unfortunately these materials contain a ZtOz second phase, possess poor mechanical strength with a low fracture toughness, have an anomalous thermal expansion behaviour, and are subject to chemical and phase instability during densification . 

Katrusiak, A. (1996d). Rigid H2O molecule model of anomalous thermal expansion of ices. 

The alteration of the O—H—O angle is indeed observed in structures in which the H atom becomes disordered (Katrusiak, 1992 1993). The O—H and H—O distances do not alter significantly when the H atom becomes disordered, and therefore - because of the altered O—H- - -O angle - the O- O distance decreases. This contraction of the O- O distance contributes to the thermal expansion of the crystal in such a way that a region of anomalous thermal expansion is observed in the direction of hydrogen bonds about the critical temperature (T. ) when the H atoms become disordered (Kobayashi, Uesu, Mizutani Enomoto, 1970 Katrusiak, 1993 Horvath, 1983 Horvath Kucharczyk, 1981). 

Figure 9.2 The anomalous thermal expansion of LaCoO and LaNby Co O ...

ANOMALOUS THERMAL EXPANSION OF THE SHORT INTERMOLECULAR BOND IN PARA-NITRaANILINE. 

ANOMALOUS THERMAL EXPANSION OF POLY/ETHYLENE TEREPHTHALATE/. 

The Fe-rich portions of several amorphous alloy systems form part of the rather seldom encountered family of materials where the concentration dependence of the magnetic moment (/t) increases while the concentration dependence of the magnetic ordering temperature (7 ) decreases. Systems showing such opposite tendencies of jti and 7 often have a further pecuhar feature associated with them, namely an anomalous thermal expansion also known as invar anomaly (Masumoto, 1931, 1934). In amorphous B, Fe . alloys such invar-type anomaUes were observed by Fukamichi et al. (1977). Similar results were obtained in amorphous Z, Fe alloys... 

The fully symmetric terms A" and A" are, however, of multi-ion origin, being related to the anomalous thermal expansion. 

Fig. 20.7. Lattice parameter vs temperature for SmS alloys substituted with different trivalent rare earth ions (left) and for Smi, GdjS alloys (middle and right). The abrupt changes in the lattice parameter are due to first-order but isostructural phase transition. To be noted is the anomalous thermal expansion (right figure) of Smi jGd,S alloys (from Jayaraman et al., 1975a).

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