Jfe Mineral Company, Ltd.

Kawatetsu Mining Co., Ltd.

Mitsuyoshi Matsushita

Yosuke Iwasaki

Yoshihito Tachi

Yousuke Iwasaki

Toshio Ogawa

A piezoelectric single crystal ingot is produced by the Bridgman method and contains a relaxor having a composition of Pb(Mg, Nb)Oand lead titanate having a composition of PbTiO. In the piezoelectric single crystal ingot, the compositional fraction of lead titanate does not vary monotonically in the growth direction of a single crystal and the variation of the compositional fraction thereof is within the range of &#xb1;2.0 mole percent over a length of 30 mm or more. A piezoelectric single crystal device is produced from the piezoelectric single crystal ingot.

Piezoelectric single crystal ingot, producing method therefor and piezoelectric single crystal device

In a piezoelectric device that uses a vibration mode in a direction parallel to a polarization direction, a single crystal device that achieves an electromechanical coupling factor of 65% or more, which is more than the electromechanical coupling factor (about 60%) of the existing flat plane type piezoelectric single crystal device in that vibrational direction, is provided by performing certain treatment to its device plane. Specifically, a piezoelectric portion having a comb-shaped structure in which a plurality of slits are formed with a certain arrangement pitch on either of device planes whose polarization direction is their normal direction, the slits having a depth extending in a direction substantially perpendicular to the device plane and being filled with an insulating material, is formed to achieve 65% or more of an electromechanical coupling factor in a direction parallel to the polarization direction.

Piezoelectric single crystal device

The present invention provides a piezoelectric single crystal device excellent in heat resistance and capable of stably maintaining the electromechanical coupling factor kin a lateral vibration mode at a high value of 50% or more without a decrease even in an operating environment in which the temperature changes from room temperature to a high temperature (specifically, 150&#xb0; C.), and also provides a fabrication method thereof. Specifically, assuming that the [101] axis of a tetragonal system having the [001] axis as a C axis (with the largest lattice constant) is a polarization direction, a normal directionto an edge face T of the piezoelectric device is within the solid-angle range of &#xb1;25&#xb0; with respect to the [-101] axis substantially orthogonal to the polarization direction, the range including the [-101] axis. Assuming that the [011] axis of the tetragonal system is the polarization direction, the normal directionto the edge face T of the piezoelectric device is within the solid-angle range of &#xb1;25&#xb0; with respect to the [0-11] axis substantially orthogonal to the polarization direction, the range including the [0-11] axis. In any case, the electromechanical coupling factor kin the direction orthogonal to the polarization direction, i.e., in the lateral vibration mode, is 50% or more.

Piezoelectric single crystal device and fabrication method thereof

To provide a piezoelectric single-crystal device which can stably attain an electromechanical coupling factor kof 60% or more in the lateral vibration mode and a method of manufacturing the same. Specifically, the piezoelectric single-crystal device has the polarization directionin the [110] axis of a pseudocubic system and has the direction normal to an end faceof the piezoelectric device within the solid angle range of the [001] axis &#xb1;35&#xb0; including the [001] axis approximately orthogonal to the polarization direction. The electromechanical coupling factor kin the direction orthogonal to the polarization direction, in the so-called lateral vibration mode, is 60% or more.

Piezoelectric single-crystal device and method of manufacturing the same

An inexpensive piezoelectric single-crystal device being excellent in the piezoelectric characteristics and having a complex perovskite structure can be provided by adding a specific additive to a lead magnesium niobate-lead titanate (PMN-PT) single crystal or a lead zinc niobate-lead titanate (PZN-PT or PZNT) single crystal. Specifically, the piezoelectric single crystal has a complex perovskite structure and is formed of a composition containing 35 to 98 mol % lead magnesium niobate [Pb(MgNb)O] or lead zinc niobate [Pb(ZnNb)O], 0.1 to 64.9 mol % lead titanate [PbTiO], and 0.05 to 30 mol % lead indium niobate [Pb(InNb)O] wherein calcium is substituted for 0.05 to 10 mol % lead in the composition.

Piezoelectric single crystal and piezoelectric single-crystal device and method for manufacturing the same

A piezoelectric single crystal device is provided exhibiting excellent piezoelectric properties, within a specific high-temperature range of Tr&#xb0; C. to (T&#x2212;20)&#xb0; C., where Trepresents a transformation temperature between a pseudocubic system and a tetragonal system. Specifically, the piezoelectric single crystal device is composed of a single crystal having a composition represented by [Pb(Mg,Nb)O]&#xb7;[PbTiO], where X is within the range of 0.26 to 0.29 and having a complex perovskite structure, wherein a specific inductive capacity at 25&#xb0; C. is 5,000 or more, and a specific inductive capacity at the transformation temperature between a pseudocubic system and a tetragonal system of the above-described single crystal is 2.5 times or more larger than the specific inductive capacity at 25&#xb0; C.

A piezoelectric single crystal device for actively employing the electromechanical coupling factor kin the direction orthogonal to the polarization direction is provided. Specifically, with the polarization direction as [001] axis of a pseudocubic system, an angle between the normal directionof the piezoelectric device edge face and the direction n orthogonal to the domain structure within the crystal face including [010] and [100] axes orthogonal to the polarization direction is in the range 0 to 15&#xb0; or 40 to 50&#xb0;.

A domain controlled piezoelectnc single crystal is disclosed which uses a lateral vibration mode for an electromechanical coupling factor k not less than 70% and a piezoelectric constant &minus;d not less than 1200 pC/N, with an electromechanical coupling factor k in the longitudinal vibration mode not less than 80% and a piezoelectric constant d not less than 800 pC/N. Also, a piezoelectric single crystal is disclosed which uses a high-performance longitudinal vibration mode with k not more than 30%. A fabrication method applies a DC electric field of 400 V/mm to 1500 V/mm for a maximum of two hours in a temperature range of 20&deg; C. to 200&deg; C. as polarization conditions in the thickness direction of the piezoelectric single crystal. The method can include cooling, or heating and cooling between temperature boundaries of rhombohedral and tetragonal crystals or between tetragonal and cubic crystals or within a cubic crystal temperature range.

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Chiba, Japan

Mitsuyoshi Matsushita