LIT-PHONON (Russia)

Summary form only given. Investigations aimed at improving crystal unit characteristics over the range 400-1000 kHz resulted in designing quartz crystals operating in a double-shear mode. The investigations were realized on the base of quartz crystal bars having a rectangular cross section of close cross sizes, with length being along X-axis. Vibrations of such bars may be approximately interpreted as a superposition of two shears-in thickness and in width of the piezoelements. Crystal units operating in the above mentioned mode have high electrophysical parameters: dynamic resistance 5-100 Ohm, motional inductance 2-20 H, quality factor 10/sup 5/-2/spl times/10/sup 6/, capacitance ratio up to 350, high temperature-frequency stability and low aging. Calculation results showed that quartz crystal units may have high temperature stability by changing the cut angle and dimensions of the piezoelements.

The optical activity change in quartz and langasite crystals and the appearance of gyration effect (rotation of the light polarization plane) in lithium niobate crystals under external load and internal stresses influence (stress-induced gyrotropy) have been investigated. The investigations have shown that internal stresses in crystals affect the gyrotropy in the same way, as the external load do. The possibility of internal stresses in crystals determination by gyration change has been discovered. Based on investigations made a method of internal stresses in these crystals has been developed. >

Technology for the synthesis and growth of langasite crystal is described. The features of the crystallization process are discussed. The main defect types of langasite crystals are defined. The results of a crystallographic investigation of langasite crystals connected with the correction of Bragg angles and angular parameters of atomic plans in this material are given. The fundamental physical properties of langasite and the application of this crystal in resonators and filters are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The results of an investigation of the electrode-quartz interface by use of the RMA method for Au, Ag, and Cu electrodes are presented. Possible reasons for the disturbed equilibrium state of the double layer are considered, e.g., under high levels of drive of the crystal unit or flashover phenomenon and electrode erosion. The mechanism for lowering crystal unit motional resistance caused by current overdrive is described. >

The investigation results of piezoelectric BAW resonators using single crystals of strong piezoelectrics are given. The possibility of face shear mode excitation in lithium tantalate piezoelectric elements of single-rotated cuts is reported which enables manufacturing resonators with zero frequency-temperature coefficients. The information regarding resonance spacing value of the resonator versus operating mode of vibration and the frequency range used is included. The realizable parameters of resonator types using lithium tantalate and La/sub 3/Ga/sub 5/SiO/sub 14/ (LGS) are also given. >