Quenched sample temperature dependences

In order to investigate the competition between magnetic interaction and spin transition in (bpym, S), quenching experiments have been performed at 0.63 GPa. Fig. 7 displays the magnetic behaviour of the quenched sample at increasing temperatures. It can be inferred from the thermal dependence of XmT that [HS-HS] entities can be frozen-in as a metastable state at low temperatures. Heating the sample above ca. 60 K leads to re-formation of... 

The phosphorescence lifetimes have been examined for many protein systems as a function of temperature. In the early work oxygen was not removed from the sample.(72,73) In these works the lifetimes are dominated by quenching by oxygen, and so the temperature dependencies probably represent temperature-dependent oxygen diffusion. 

These factors are consistent with the 10- to 20-fold decline observed in polyselenide electrolyte in those experiments there also appeared to be little potential dependence of the results (9). Similar thermal quenching data has been reported for dry CdS Te samples irradiated with UV light (10,12,13), electron beams (11), and a particles (19). The temperature dependence of the decline in emission intensity has been linked to the ionization energy of the Te-bound hole, 0.2 eV (10,11,12,13,19). 

In the diagram, phase boundaries have been indicated by vertical lines, since their dependence upon temperature during reheating of a quenched sample is not known. 

A consequence of the afore-mentioned slow transitions would be a rather strong dependence of the actual structure observed at room temperature upon the previous thermal history of the sample. For example, quenched samples around Na0i35WO3 may be cubic, while slowly annealed samples would be tetragonal (II). Conversely, samples of low sodium content may be cubic if they have been prepared by extracting sodium vapor at temperatures of 600° to 700°. The existence of two-phase regions may account for some of the difficulties we (and others) have had in growing single crystals of low-sodium bronzes by the electrolytic method. 

CP/MAS and PST/MAS NMR spectra of nylon 6 single crystals sample, melt quenched sample, and drawn sample at room temperature (the carbonyl peak is not shown because a single sharp line appears without significant change for all samples). The lineshapes of the CHa peaks depend on the crystallization conditions, and, furthermore, those for the same sample obtained by CP/MAS and PST/MAS are markedly different. It is noted that the PST/MAS method, in contrast to the CP/MAS method, enhances the peak intensity for CHa carbons, such as those in the noncrystalline state, which undergo relatively rapid reorientation. Therefore, a comparison of C CP/MAS and PST/MAS spectra leads to a discussion of the structure and dynamics of the crystalline and noncrystalline states in nylon 6 sample crystallized under various conditions. The C chemical shifts are listed in Table... 

Another rather large category of acceptors is produced when germanium samples containing group-I or TM elements are annealed at temperatures above 850°C and quenched to RT. From the temperature dependence of the Hall effect, centres produced by this method were labelled as SAi and SA2,... 

The temperature dependences of the IR bands of PE were quite different for the slow-crystallized and quenched samples. This effect was most noticeable for the crystalline rocking modes. The peak heights of the 720 and 731 cm" components of this doublet increased with increasing temperature. This was not as anticipated. The intermolecular forces lessen with thermal expansion. Therefore, the induced dipole moment of the interaction decreases with increasing temperature (45,46). The intensity of a band which is enhanced by the dipole-dipole interaction is expected to decrease. 

PD8S. The large variation in the phase transition temperatures and other physical properties such as UV absorption as reported by different authors indicates a rich polymorphism of this polymer. Very recently, Chunwachirasiri et al. reported on five different crystalline or semicrystalline structures in quenched samples of PD8S, some of which occur only below the temperature range considered here. Our own DSC experiments on samples prepared in three different ways (denoted A-C) confirm that the phase behavior strongly depends on the conditions of sample preparation. 

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