Abstract
We present a possible method to reduce the anisotropy of the thermal stress generated on langasite-type La3Ta0.5Ga5.5O14 (LTG) piezoelectric crystals arising from the mismatch of the thermal expansion coefficients and Young’s moduli of the crystals and metals at high temperatures. To formulate this method, the thermal stresses of order-type langasite crystals, in which each cation site is occupied by one element only, were calculated and compared to each other. Our results suggest that the largest cation site affects the thermal stress. We attempted to replace La3+ in LTG by a larger ion and considered Sr2+. Single crystals of strontium-substituted LTG (Sr-LTG) were grown using the Czochralski method. The thermal stress along the crystallographic c-axis decreased but that perpendicular to the c-axis increased by strontium substitution into the LTG crystal. The anisotropic thermal stress was reduced effectively. The Sr-LTG single crystal is a superior candidate material for pressure sensors usable at high temperatures.
Highlights
In recent years, the automobile industry has been faced with a number of environmental and energy problems
First, we describe the calculation of the thermal stress using the data of the linear thermal expansion coefficients and elastic stiffness coefficients instead of the Young’s moduli, of four order-type langasite family crystals and the metal at high temperatures
We formulated a method to reduce the anisotropy of the thermal stress generated on LTG crystals when the LTG crystal was used as a combustion pressure sensor
Summary
The automobile industry has been faced with a number of environmental and energy problems. Improvements to fuel efficiency and reduction in exhaust gas have been required [1]. Combustion pressure sensors are attractive devices for improving the combustion efficiency of engines. Such devices are directly placed in engine cylinders and combustion efficiency is improved by feedback control of the fuel injection based on data of the combustion pressure changes in the cylinder. An engine with a combustion pressure sensor can reduce NOx emissions by approximately. La3 Ga5 SiO14 (langasite) family single crystals are attractive piezoelectric materials for use in combustion pressure sensors because they show no phase transitions up to their melting temperature and can be grown to large sizes using the Czochralski (Cz) technique [3,4,5,6,7,8,9].
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