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Langasite and Langatate
Lanthanum gallium silicate ( La2Ga5SiO14 ), or langasite / LGS is a phenomenal invention. Though langasite was initially developed as a laser crystal, it revealed a remarkable combination of piezoelectric qualities, which opened up new opportunities to use the LGS crystal in radio frequency devices. The main applications of langasite crystals now is SAW filters and SAW resonators. Experts agree that LGS is the best choice for high-efficiency broad band frequency devices because it possesses exceptional frequency-temperature characteristics, a very high index of electromechanical coupling and un unparalleled Q-factor.
Lanthanum gallium tantalite (La3Ga5.5Ta0.5O14), or langatate (LGT) is gaining popularity with manufacturers of control and measurement devices. Pressure and vibration sensors produced on the basis of langatate show excellent performance at temperatures up to 600°C, and experts say that a langatate sensor operating at up to 900°C is likely to emerge in the near future.

Basic properties

Crystal Structure trigonal system, group 33
a= 8.1783 c = 5.1014
Growth Method Czochralski  
Hardness 6.6 Moh's 
Density 5.754 g/cm3 
Melt Point 1470 o C ( phase transition point: N/A) 
Thermal expansion (x10-6/ oC) α 11: 5.10 α 33: 3.61 
Acoustic velocity, SAW 2400 ( m/sec ) 
Frequency constant, BAW 1380 ( kHz/mm ) 
Piezoelectric coupling K2 (%) BAW: 2.21 SAW: 0.3  
Inclusions N0 

Comparison of Piezoelectric Crystals Used for SAW Applications
Langasite, La2Ga5SiO14 Quartz, SiO2Lithium tetraborate, Li2B2O3Lithium tantalate, LiTaO3
Index of el.mech. coupling Kemc, %
Frequency spacing Δf, % 0.900.254.007.00
Q-factor Q, x1035010010
Temp. frequency coef., TFC, x10-1 °C

Comparison of Surface Waves in Quartz and Langasite
Characteristics Quartz, SiO2LGS,La2Ga5SiO14
Vef 0°, 132.75°, 0° 0°, 140°, 22.5° 0°, 140°, 25°
K2emc 0,14 0,32 0,38
SAW velocity 3157 2742 2736
a2 x 108/°C2 -3.2 -7.8 -6.8
TT,°C (temp. coef.) 25 25 23
E (dielectric const) 4,92 - 27
M, degr. (power flow angle) 0 52 51
Langatate Comparison of Piezoelectric Crystals Used for Pressure and
Vibration Sensors
Langatate La3Ga5.5Ta0.5O14Quartz, SiO2APC-850 N-2APC-856
Relative dielectric constant K=εT 33/ε0, 1 80.3 4.6 1750 4100
Curie point Tc, °C -570360150
Piezoelectric charge constant, 10-12 C/N or m/Vz ___ 
-d11 6.52.3d33=400d33=620
d14 4.70.9d15=590d15=710
Piezoelectric voltage constant, 10-3 Vm/N or m2/C ___ 
-g11 3858g33=26g33=18.5
g14 27.718g15=36g15=25
Young modulus, 1010 N/m2 ___ 
YE33 1910.45.44.5
Frequency constants, Hz-m or m/s ___ 
Longtitudal mode NL 2870-1500-
Thickness mode NT 1320166620321980
Elastic compliance, 10-12 m2/N ___ 
SE11 9.012.815.315.0
SE33 5.29.617.317.0
Density ρ, g/cm3 6.132.657.77.5
Q-value Qm, 1 500001068072


Langasite as-grown Boules
Diameter/Width 80-100 mm
Thickness/Length Up to 150 mm
Orientation along <00.1>, <01.1> and <11.0> axis
Surface quality As-grown

Langasite Substrates for SAW Applications
Diameter 76.2-101.4 mm
Thickness 0.5 mm
Orientation Primary flat is perpendicular to X' axis with accuracy ±15 min, Yxlt/48.5°/26.6°
LTV 2.2 microns for the base 20 mm X 20mm
Surface quality No dimples, cracks, unpolished areas, contaminants in working area under x50 magnification. Scratches visible at x50 magnification are allowed in working area if their quantity is lower than 3 on one wafer and less than 20 in a lot of one hundred wafers.
Edge chipping No chipping inside the working area and on the primary flat. Chipping can be accepted outside the working area if the width is less than 0.5 mm, and the cumulative length is less than 5 mm.
Working face Working area: wafer diameter minus 3 mm

Langatate blocks and plates for sensing parts
Diameter/Width Up to 80 mm
Thickness/Length, X-cut 5-30 mm
Thickness/Length, Y-cut 5-30 mm
Thickness/Length, Z-cut Up to 100 mm

Langatate sensing parts
Outer diameter 6-15 mm
Inner diameter 3-6 mm
Thickness >=0.15 mm



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