HIGHLY INSULATING/HIGHLY STABLE PIEZOELECTRIC LTGA SINGLE CRYSTAL, METHOD FOR PRODUCING SAME, PIEZOELECTRIC ELEMENT USING SAID LTGA SINGLE CRYSTAL, AND COMBUSTION PRESSURE SENSOR

摘要

In accordance with the present invention, there is provided a method for producing a single LTGA crystal from a polycrystalline starting material prepared from a mixture of La2O3, Ta2O5, Ga2O3, and Al2O3, wherein a mixture having a composition represented by y(La2O3) + (1-x-y-z)(Ta2O5) + z(Ga2O3) + x(Al2O3) (in the formula, 0 x ≤ 0.40/9, 3.00/9 y ≤ 3.23/9, and 5.00/9 ≤ z 5.50/9) is used as the polycrystalline starting material, and a single LTGA crystal is grown using the Z-axis as a crystal growth axis. The grown LTGA single crystal is preferably subjected to a vacuum heat treatment. The single LTGA crystal grown by the method according to the present invention, which is highly insulative and highly stable, can be utilized in such applications as a piezoelectric element of a highly reliable combustion pressure sensor useful in measurement of a combustion pressure in a combustion chamber of an internal combustion engine.