INFLUENCE OF CHEMISTRY ON THE PYROELECTRIC EFFECT IN TOURMALINE

Pyroelectric coefficients were measured from a series of natural tourm aline crystals between similar to 170 and similar to 500 K to quantify the variation of the pyroelectric effect with chemical composition. T he amount of Fe in tourmaline has a prominent influence on the pyroele ctricity. Fe content linearly decreases the pyroelectric coefficient i n the composition range between 0.01(1) and 14.6(2) wt% FeO. Thus, to a first approximation, tourmaline pyroelectric coefficients may be pre dicted directly from the chemical composition derived by routine elect ron probe microanalysis. The relationships between pyroelectricity and chemistry indicate that the pyroelectric coefficient is influenced to different extents by the occupancies of the X, Y, and Z cation sites in the tourmaline structure. The octahedral Y site occupancy strongly influences the pyroelectric coefficient due to the preference of Fe fo r this site. This work further suggests that the addition of Fe and Mg cations to the smaller Z octahedral site causes the pyroelectric coef ficient to increase. However, because an extended suite of samples is not available in which the Z site contains ions other than Al, this pr oposed trend has not been experimentally determined. The chemistry of the ninefold coordinated X site and the population of this site do not influence the pyroelectric coefficients of tourmaline.