Synthetic Quartz Crystal

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Synthetic Quartz Crystal:

A single crystal grown using the

hydrothermal synthesis method.

As-Grown Quartz Crystal

: A synthetic quartz crystal grown

naturally with no processing.

Lumbered Quartz Crystal:

A synthetic quartz crystal with the X

and Z surfaces processed according to specified dimensions

and angles using a diamond wheel #80.

Y-bar Synthetic Quartz Crystal:

A synthetic quartz crystal grown

by using a bar-like seed crystal elongated in the Y-axis direction.

Z-plate Synthetic Quartz Crystal:

A synthetic quartz crystal

grown by using a plate-like seed crystal with a Y-axis direction

length and X-axis direction width.

Inclusion:

A general term for solid constituents (inclusions) that

exist in synthetic quartz crystal; they can be observed when light

is scattered through a liquid with a refractive index that is close

to that of the synthetic quartz crystal. Main inclusions are acmite

and emeleusite. They are generated by the chemical reaction of

Fe within an autoclave and synthetic quartz crystal growth

frame, Na from a solution, SiO

of a material, etc. at high

temperature and under high pressure.

Twins:

Crystallographically, taking into account specific facets or

axes two or more crystals are symmetrically joined to one

crystal. Almost all twin crystals that are generated as synthetic

quartz crystals are electrical ones, and electrical twin crystals

affect the shape of the synthetic quartz crystal. They can easily

be identified visually.

Right-handed and left-handed quartz crystals:

Crystals are

divided into two types: right-handed and left-handed. A

difference in optical rotation creates the 2 types, but their

physical properties are identical. Therefore, by cutting at the

correct angle, the difference does not affect the characteristics

of a crystal oscillator. Generally right-handed quartz crystals are

used in manufacture.

Zone:

A zone with a crystal that has grown from a seed crystal at

its core. There are Z, +X, -X, and S zones.

Infrared Absorption Coefficient

This value measured with an

infrared spectrophotometer is adopted as the infrared absorption

coefficient α of a synthetic quartz crystal. The value is based on

the absorption characteristic of the OH radical of a synthetic

quartz crystal that is around 3,800 to 3,000 cm

–1

of the infrared

transmittance curve. Generally, absorption coefficients with

wave numbers 3585, 3500, and 3410 cm

–1

have been adopted.

(As is usual practice, an infrared Q value is also described for

reference.)

Etch Channel:

Tubular cavities generated along linear defects in

a crystal when the crystal is etched. When the processing of a

crystal piece for manufacturing a tuning fork-type crystal

oscillator or a reversed mesa-type involves etching, a synthetic

quartz crystal with a low etch channel density is particularly

suitable.

Y axis

X axis

Synthetic and natural right-handed

and left-handed quartz crystals

Relationship between synthetic

and natural quartz crystals

m surface

R surface

Z axis

r surface

Left-handed quartz crystal Right-handed quartz crystal

Terms and Definitions

Synthetic Quartz Crystal

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Properties of Quartz Crystal

Precautions for Use

How to Manufacture Synthetic Quartz Crystal

Constituent: SiO

Crystal system: Trigonal system

Crystallographic group: D

(32)

Lattice constant: a = 4.9027 + 70×10

–6

(T−18) kX

c = 5.3934 + 47×10

–6

(T−18) kX

1kX = 1.002063±0.000007Å

Density: 2.649 g/cm

α–β phase transition temperature: 573 °C

Synthetic quartz crystal is manufactured in a vertical-type

autoclave (high-temperature and high-pressure oven) using the

hydrothermal synthesis method. An autoclave is partitioned by a

baffle into two compartments: an upper and lower. Seed crystals

are placed in the upper compartment (growth zone) and materials

(lascas) in the lower (dissolution zone).A dilute alkaline solution is

then poured into the remaining 60 to 80 percent of free space and,

after being covered the autoclave is heated with a heater.

When the temperatures of the upper and lower compartments of the

autoclave reach between 300 to 320 °C and 380 to 400 °C, respectively,

the alkaline solution expands and is compressed; the pressure inside

reaches 130 to 145 MPa.

Under these high temperatures and pressures the materials in the

lower compartment of the autoclave dissolve in the alkaline

solution to become an SiO

saturated solution. This saturated

solution rises due to the convection caused by the temperature

difference between the upper and lower compartments of the

autoclave. When the solution reaches the upper compartment of

the autoclave, it becomes supersaturated because of the lower

temperature of the compartment, and according to the degree of

the temperature difference SiO

is crystallized on the seed crystal.

The solution then returns to the lower compartment of the

autoclave and dissolves the materials, thereby becoming an SiO

saturated solution, and due to convection it rises and the cycle

repeats. The repetition of this process leads to the successive

growth of synthetic quartz crystals.

Make sure to read the following carefully before using synthetic

quartz crystals:

Crystal quartz changes from α crystal to β quartz crystal at a

temperature of 573° C because of phase transition. This phase

transition is reversible, but transition from β quartz crystal to α

crystal does not take place homogeneously, and twins are

created. Therefore, careful attention must be paid to never allow

the temperature to rise above 573 °C.

Pressure gauge

Safety valve

Autoclave cover

Clamp

Band heater

Gray seal ring

Thermocouple

Seed crystal

Thermocouple

Baffle

Thermocouple

Materials (lascas)

Thermocouple

Schematic depiction of synthetic quartz crystal growth

Autoclave main body