US3894846A - Method of producing single crystals of gadolinium molybdate family - Google Patents

Method of producing single crystals of gadolinium molybdate family Download PDF

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US3894846A
US3894846A US440359A US44035974A US3894846A US 3894846 A US3894846 A US 3894846A US 440359 A US440359 A US 440359A US 44035974 A US44035974 A US 44035974A US 3894846 A US3894846 A US 3894846A
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single crystal
cooling
temperature
rate
molybdate
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Kazuyuki Nagatuma
Seikichi Akiyama
Hirotugu Kozuka
Masayoshi Kobayashi
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Hitachi Ltd
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Hitachi Ltd
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Priority claimed from JP12167173A external-priority patent/JPS5324040B2/ja
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/16—Oxides
    • C30B29/22—Complex oxides
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/16—Oxides
    • C30B29/22—Complex oxides
    • C30B29/32—Titanates; Germanates; Molybdates; Tungstates
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure

Definitions

  • ABSTRACT A method of producing the single crystals of the gadolinium molybdate family having a high transmission and low threshold field, comprising the step of growing a single crystal from a melt of the gadolinium molybdate family by a crystal pulling technique, the step of cooling slowly the single crystal in a temperature range of from immediately below a melting point to a segregation temperature of a phase of the single crystal and the further step of cooling under such cooling conditions that the a phase is not segregated and the value of the threshold field of the single crystal is not made large in a temperature range of below the segre gation temperature of the a phase.
  • the present invention relates to a method of producing single crystals of the gadolinium molybdate family, more particularly the single crystals having a high transmission and a low threshold field.
  • the single crystals of gadolinium molybdate family for example, a gadolinium molybdate (Gd (MoO single crystal, are produced by heat-melting a polycrystal of gadolinium molybdate or a mixture consisting of molybdenum oxide and gadolinium oxide which is so compounded as to satisfy a stoichiometric value as constitutes gadolinium molybdate, by immersing a seed crystal in the resultant melt, by growing the single crystal of gadolinium molybdate with the crystal pulling technique, and thereafter by cooling the single crystal from a high temperature to room temperature.
  • Gadolinium molybdate Gadolinium molybdate
  • the inventors have previously proposed a method in which the cooling rate in the cooling process after growing the gadolinium molybdate single crystal from the melt by the crystal pulling technique is made large, thereby to produce an optical material of sufficiently high transmissron.
  • the gadolinium molybdate single crystal is to be employed as the material of an electro-optical element such as optical shutter, light modulator and color modulator, it is desired that besides a high transmission that the threshold field is low while the mobility is high.
  • the terms threshold field" and mobility mean the point (1) of intersection with the axis of abscissas as obtained by the extrapolation and the inclination tan 6 of a characteristic straight line, respectively, in the characteristic of electric fields transfer velocity of a polarization wall (wall velocity) as shown in FIG. 1.
  • the gadolinium molybdate single crystal obtained by the process mentioned above has a large threshold field, therefore it cannot be used in an electro-optical application.
  • the primary object of this invention is to provide a method in which the single crystals of gadolinium molybdate family having a high transmission and a low threshold field are produced.
  • Another object of this invention is to provide a method in which single crystals of gadolinium molybdate family that may be employed as a material of the electro-optical element are produced.
  • Still another object of this invention is to provide a method in which the single crystals of gadolinium molybdate family are produced by specifically giving appropriate conditions in the cooling process thereof.
  • Yet another object of this invention is to provide a method in which the single crystals of gadolinium molybdate family having a high transmission and a low threshold field from the single crystal manufactured by the steps of heat-melting polycrystal of gadolinium molybdate or a mixture consisting of molybdenum oxide and oxide of one of the group consisting of gadolinium, europium, dysprosium and terbium that is so compounded as to satisfy a stoichiometric composition as constitutes molybdate, immersing a seed crystal in the melt obtained, and growing the single crystal of molybdate by the crystal pulling technique.
  • a further object of this invention is to provide a method in which single crystals of gadolinium molybdate family having a high transmission and a low threshold field are obtained from the single crystal having large threshold field in a wall transfer.
  • the method of producing single crystals of gadolinium molybdate family of the present invention is characterized by comprising the step of growing the single crystal from a melt of the gadolinium molybdate family by the crystal pulling technique; the step of cooling slowly the single crystals in a temperature range of from immediately below a melting point to a segregation temperature of the or phase of the single crystal and the further step of cooling under cooling conditions such that the a phase is not segregated and the value of the threshold field of the single crystal is not made large in a temperature range below the segregation temperature of the 0: phase.
  • the threshold field between the threshold field and the cooling rate in the cooling process after growing the single crystals of the gadolinium molybdate family from the melt by the crystal pulling technique, there is the relation that as the cooling rate is larger, the threshold field is higher. Between the threshold field and the mobility, there is the relationship that as the threshold field is lower, the mobility is higher.
  • the cooling rate in the cooling process need be made large in order to achieve a single crystal of high transmission as mentioned above, the cooling rate needs to be made small in order to achieve the single crystal of low threshold field; the cooling process being performed from the high temperature to room temperature after hot-melting the polycrystal of gadolinium molybdate family (or a mixture consisting of molybdenum oxide and oxide of one of the group consisting of gadolinium, europium, dysprosium and terbium that is so compounded as to satisfy the stoichiometric value as constitutes gadolinium molybdate family) and after growing the single crystal of gadolinium molybdate family by the crystal pulling technique with the seed crystal immersed in the resultant melt.
  • thermodynamic stable phase of gadolinium molybdate below 850C. is the a phase
  • the phase to be used for the material of the electro-optical element is the metastable phase.
  • it is presumed that it takes about 25,000 years for this phase to be transitet. to the a phase at room temperature, and it has been revealed that this phase may practically be handled as the stable phase.
  • Powder of 1 mole of gadolinium oxide and 3 moles of molybdenum oxide compounded was sufficiently ground and mixed.
  • the powder was gradually heated for at least 36 hours, and it was melted at l,l60C.
  • a seed crystal having [I10] direction was fixed to a platinum holder, and it was immersed in the melt. While the holder was being rotated at a number of revolutions of I r.p.m., it was pulled up to the pull-up rate of 14 min/hr. to grow a cylindrical single crystal of gadolinium molybdate being about l5 mm. in diameter and about 50 mm. in length. Thereafter, the single crystal was cut away from the melt.
  • the crystal was held at about I,000C., it was cooled down to 200C. immediately before the Curie point (approximately I60C.) at a constant cooling rate and then cooled down to the room temperature at the cooling rate of l20C./hr.
  • the transmission of the single crystal thus obtained is plotted as the function of the cooling rate in FIG. 2.
  • the transmission is depicted as a ratio of transmissive light quantity to incident light quantity per 1 cm. in thickness.
  • line 2 depicts the trans mission in the case the light absorption of the single crystal is zero.
  • the transmission increases more as the cooling rate is greater, but it has a substantially constant value above 400C/hr.
  • the transmission of at least 70% is required for use of a material of an electro-optical element.
  • the cooling rate need be at least 250C./hr. in order to render the transmission 75% or higher.
  • a I-le-Ne laser having an output of 5 mW and a wavelength of 6,328A was used as a light source, and the thickness of specimen was made cm.
  • the relationship between the threshold field and the cooling rate is illustrated in FIG. 3. As the cooling rate becomes greater, the threshold field increases.
  • the threshold field at the cooling rate of 800C./hr. is twice as high as that at the cooling rate of 20C./hr. It can therefore be concluded that the cooling rate cannot be made very large in order to apply the single crystal to a low-voltage light valve.
  • the measurements of the threshold fields were carried out in such way that positive and negative pulse voltages were applied to specimens of a thickness of 0.8 mm. as obtained by cutting the produced single crystal and subjecting the sliced pieces to optical polishing and the current waveforms of polarization reversal flowing through an electric resistance connected in series with the specimens were read by means of a memory scope.
  • FIGS. 46140 The X-ray diffraction peaks of a single crystal at various cooling rates are as shown in FIGS. 46140.
  • FIG. 4a the X-ray diffraction peaks of a single crystal which became whitish at a very small cooling rate is shown,
  • FIG. 40 includes Xray diffraction peaks not present in FIG. 4b. Something corresponding to these X-ray diffraction peaks is considered to be the substance which induces the whitening.
  • X-ray diffraction peaks appearing only in a temperature range of from the room temperature to 850C. are noted.
  • FIG. 40 These X-ray diffraction peaks correspond to the so-called a phase which is the thermodynamic theoretical stable phase at temperatures below 850C. It can be considered that the X-ray diffraction peaks in FIG. 4c and those in FIG. 4b as added up are the X-ray diffraction peaks in FIG. 4a.
  • FIG. 2 is nothing but a representation of the relationship between the cooling rate and transmission in the range of temperatures below 850C.
  • the transmission is determined by the cooling rate in the temperature range below 850C. (the segregation temperature of a phase of gadolinium molybdate).
  • 850C. the segregation temperature of a phase of gadolinium molybdate.
  • FIG. 3 it is seen from FIG. 3 that in the case of cooling the crystal at the constant cooling rate from about 1,000C. to the temperature immediately before the Curie point, when the cooling rate is small the threshold field is small.
  • the cooling rate at high temperatures will have a greater influence on the threshold field than the cooling rate at low temperatures wil, and it has been verified that the cooling rate in the temperature range above 850C. affects the threshold field more strongly than the cooling rate in the temperature range below 850C.
  • the above-mentioned is a method that relates to a single crystal cooled from above the segregation temperature of the single crystals of the gadolinium molybdate family in the crystal pull technique, but this method can be used to produce the single crystals of the gadolinium molybdate family having high transmission and low threshold field from single crystals of gadolinium molybdate family having high threshold field.
  • a step in which the single crystal having high threshold field is heat-treated for a predetermined time in the temperature of immediately below the melting point of the single crystal is added.
  • the transmission approaches to the theoretical value as the cooling rate becomes large.
  • the single crystal of the gadolinium molybdate produced thus has a sufficiently large transmission, homogeneity and a variation of a double refraction index of under l, it is used for a stationally phase controlling optical element (the passive optical element), for example, a half-wavelength plate which can be used the same as mica, quartz.
  • the passive optical element for example, a half-wavelength plate which can be used the same as mica, quartz.
  • the gadolinium molybdate single crystal is used as a material of the electro-optical element (such as optical shutter, light modulator and color modulator) it is desired that beside the transmission that the threshold field is low, while the mobility is high (as mentioned above). It is effective that the cooling time of the single crystal after growing is short in efficiency of time from an industrial standpoint.
  • the electro-optical element such as optical shutter, light modulator and color modulator
  • the single crystal having the high threshold field can be improved in optical, electrical and mechanical properties.
  • the single crystal having high transmission and low threshold field could be produced with good reproducibility by applying the above conditions to the crystal production.
  • FIG. 1 is a diagram of the characteristic of the electric field wall velocity for explaining the threshold field and the mobility
  • FIG. 2 is a diagram of the characteristic of cooling rate-transmission
  • FIG. 3 is a diagram of the characteristic of cooling rate-threshold field
  • FIGS. 4a, 4b and 4c are diagrams of X-ray diffraction peaks of the single crystal at various cooling rates
  • FIG. 5 is a characteristic diagram representing the relationship between the cooling condition and the threshold field in the method of producing the single crystal of gadolinium molybdate according to the present invention
  • FIGS. 6, 7 and 8 are diagrams of the changes-with time of the temperature, each illustrating cooling con ditions in an example of the present invention
  • FIGS. 9, I0 and 11 are other diagrams of the changes-with-time of the temperature, each illustrating cooling conditions in an example of the present invention.
  • FIG. 12 is a characteristic diagram representing the relationship between the cooling condition in FIG. II and the threshold field and the transmission;
  • FIG. 13 is a characteristic diagram representing the relationship between the heat treatment temperature and the heat treatment time in improving the single crystal oflarge threshold field according to the present invention.
  • FIG. 14 is a characteristic diagram representing the relationship between the cooling conditions and the threshold field in the method of producing the single crystal of gadolinium molybdate according to the pres ent invention.
  • FIG. 15 is a characteristic diagram representing the relationship between the cooling condition and the transmission in the method of producing the single crystal of gadolinium molybdate according to the present invention.
  • the single crystal of gadolinium rnolybdate was grown, cut away from the melt and held at about l,000C. Thereafter, the single crystal was cooled at a constant cooling rate in the temperature range above 850C, it was cooled at a greater constant cooling rate in a range of temperatures of 850C. 200C, and it was cooled at the cooling rate of l20(../hr. in a range of temperatures of 200C. the room temperature. This experiment was repeated numerously, and the relationship between the cooling conditions and the threshold field (as shown in FIG. 5) was obtained.
  • the axis of ordinates represents the cooling rates in the temperature range above 850C
  • the axis of ahscissas represents the cooling rates in the temperature range of 850C 200C
  • numerical values represent.
  • the values of the threshold fields in the unit of V/cm). Each of the values is a mean value by five or more trials. and has a dispersion of within i 10%.
  • the marks in the Figure denote the measured values in the case where the single crystal was cooled 7 at the constant cooling rate from the high temperature to 200 C., that is, the measured values in FIG. 3.
  • a transmission of at least 70% is generally required in case of employing the single crystal as the material of the electro-optical element.
  • the cooling rate in the temperature range of 850C. 200C. need be greater than 250C/hr. on the basis of the results shown in FIG. 2.
  • the value of the threshold field in the case of uniformly cooling the single crystal from about l,000C. down to 200C. at the cooling rate of at least 250C/hr. is 650 V/cm or larger as seen from FIG. 3 or FIG. 5.
  • the value of the threshold field can be lowered to 500V/cm or so with the transmission maintained at 70% or higher.
  • the single crystal being of good quality both optically and electrically is obtainable by the cool ing conditions within a region A which is surrounded by the straight line 3, the curve 4 and the axis of abscissas in FIG. 5.
  • the point P indicates that the value of the threshold field is 530 V/cm at the time when the cooling rate is 25C./hr. in the temperature range above 850C. and 400C./hr. in the temperature range of 850C. 200C.
  • the change-with-time of the temperature of the point P is illustrated in FIG. 6.
  • the transmission of the point P has the saturation value of 78% as seen from FIG. 2.
  • Example 2 In the performance of Example I, the cooling process after growing the single crystal was divided for the temperature ranges of (1) above 850C., (2) 850C. 200C. and (3) below 200C, and the cooling rates in the temperature ranges of (1) and (2) were changed variously. In the performance of the present example, the temperature ranges divided were of (1) above 850C., (2) 850C.-500C and (3) below 500C.
  • the single crystal of gadolinium molybdate was grown, cut away from the melt and held at about l,000C. Thereafter, the single crystal was cooled (l) at the cooling rate of 25C/hr. in the temperature range of above 850C., (2) at the cooling rate of 400C.,/hr. in the temperature range of 850C. 500C, and (3) at the cooling rate of 120C/hr. in the temperature range of 500C. the room temperature. These cooling conditions are illustrated in FIG. 7. This trial was repeated 5 or more times.
  • Example 2 into which the straight line-like temperature changes in Example 2 were smoothed were bestowed on the single crystal.
  • EXAMPLE 4 The above examples illustrate a cooling condition which was maintained at about 1,000C after growing of the single crystal of gadolinium molybdate.
  • the single crystal gadolinium molybdate grown in the crystal pull technique and being at about 1,000C. is cut away from the melt and is transferred to a thermal resistance furnace placed in the upper part of the growing device and is maintained at a suitable temperature time at immediately below the melting point.
  • the single crystal gadolinium molybdate is grown as in the above Examples.
  • the single crystal at about l,000C. temperature and cut away from the melt after growing was transferred slowly to the thermal resistance furnace being provided in the upper part of the growing device and maintained at a temperature range of 1 C. 1 C.
  • the single crystal was cooled at the cooling rate of 25C./hr. in the temperature range of above 850C (i.e. from about l,l50C. 850C.), at the cooling rate 400C/hr. in the temperature range of 850C. 500C. at the cooling rate 400C/hr. in the temperature range of 850C.-500C. and at the cooling rate of 120C/hr. in the temperature range of 500C. the room temperature.
  • the thermal maintenance and cooling conditions are illustrated in FIG. 9. This trial was repeated five times.
  • the process to cooling after maintaining the single crystal for 4 hours at the temperature range of l,l40C. l,l50C. is effective to improve the threshold field and the single crystal obtained was good optically.
  • the cooling rate in the temperature range 200C. room temperature was constant at about l20C./hr.
  • This cooling rate is due to that the gadolinium molybdate has the ferroelectric and ferroelastic phase transition point at about C; hence, the change of thermal expansion at neighboring 160C. is large (S. E. Cummins; Ferroelectrics II l970]p. ll 17), therefore, when the cooling rate is as large as about l60C, cracks may be introduced in the single crystal.
  • the single crystal was maintained at l,000C.; thereafter, the single crystal was cooled at the cooling rate of 25C./hr. in the temperature range of l,000C. 850C., at the cooling rate of 400C./hr. in the temperature range of 850C. 200C. and at five cooling rates of 50C./hr., lOC./hr., 200C.,/hr, 400C./hr., l,000C./hr. in the temperature range of 200C. room temperature. This trial was repeated five times, respectively. FIG, shows the results of these cooling conditions.
  • EXAMPLE 6 This Example is a variation of Examples 1 and 2.
  • the single crystal was cooled at the cooling rate of 25C./hr. in the temperature range of l,000C. 850C, at the cooling rate of 400C./hr. in the temperature range of 850C. TC.(850C. T the room temperature), and at the cooling rate of l20C./hr. in the temperature range of TC. the room temperature.
  • FIG. II shows the cooling conditions examined.
  • FIG. I2 shows the relationship between the threshold field and the transmission of the single crystal obtained and the temperature TC.
  • Example 7 Powder containing l mole of gadolinium oxide and 3 moles of molybdenum oxide compounded together was sufficiently ground and mixed.
  • the powder was gradually heated for at least 36 hours in a high frequency heating single crystal pulling apparatus, and it was melted at l,l60C.
  • a seed crystal having [l 101 direction was fixed to a platinum holder, and it was immersed in the melt. While the holder was being rotated at the number of revolutions of I20 r.p.m., it was pulled up at the pull-up rate of IO mm/hr.
  • the single crystal was cut away from the melt.
  • the heat source in the heating device cut off and thereafter the single crystal was cooled at the cooling rate of 2,000C./hr. in the temperature of about 850C, at the cooling rate of I ,000C./hr. in the temperature of about 500C, at the cooling rate of 200C./hr. in the temper ature of about 200C. That is, the single crystal was cooled naturally at the cooling condition having an exponential function, i.e., having a large cooling rate at or in the high temperature. The trial was repeated 20 times, and single crystals were obtained.
  • the transmission of the single crystal thus obtained was shown 78% i 1% in the transmission as relative the transmissive light quantity to the incident light quantity per l cm in thickness and the threshold field of the single crystal thus obtained was shown 900 t 10 V/cm.
  • a He-Ne laser having an output of 5mW and a wavelength of 6328 A was used as a light source, and the thickness of specimens was made 1 cm.
  • LiCl liquid electrode, the pulse voltage and memoryscope were used for the measurements of the threshold field in the wall transfer. The sample used was the single crystal which had a thickness made 0.8 mm by cutting away and polishing.
  • the threshold field of the single crystal gadolinium molybdate before giving the heating and cooling treatment was 900 i 10 V/cm. but as clear from FIG. 13, when the treatment range is selected in area B surrounded by curve 5, the threshold field can be decreased remarkably.
  • Example 8 As in Example 7, a single crystal gadolinium molybdate was grown and cooled, and from the single crystal, 20 single crystals having dimensions of about l0 mm in thickness, about 25 mm in width and about mm in length were provided.
  • the single crystals provided thus had the transmission in relative transmissive light quantity to incident light quantity (thereafter it is called the relative transmission) per 1 cm in thickness of 78% t 10%, and a threshold field of 900 i 10 V/cm (it was measured by the single crystal of 0.8 mm in thickness).
  • Example 7 the heat treated prism-like single crystal obtained was measured for the relative transmission, and further the single crystals were made to a single crystal plate of 0.8 mm in thickness and the threshold field was measured.
  • FIG. 14 illustrates the relative transmission per 1 cm
  • FIG. 15 illustrates the threshold field of the single crystal plate of 0.8 mm in thickness.
  • the cooling rate under 200C. is fixed at lC./hr. because it is necessary to cool at a cooling rate of under 200C./hr. so that when the single crystal passes through the ferroelectric and ferroelastic transition point at 160C, the single crystal is not destroyed. This is due to the fact that cooling conditions under 200C. do not affect the character as mentioned above.
  • the temperature range for cooling was divided by the three steps of the melting point 850C, 850C 200C., 200C. the room temperature, and the cooling rate is afforded suitably in each step. But it can be used to any variation that the 01 phase is not precipitated and the value of the threshold field is not made large.
  • the cooling rates are governed in part by the temperature ranges under consideration. For example, in the preferred embodiment shown in FIG. 5, the cooling rate above 850C. is less than 250C./hr. and the cooling rate in the temperature range of from 850C. to 200C. is from 250C. to l,l00"C./hrv
  • the single crystals of the gadolinium molybdate family obtained by this invention will have transmission values over about and threshold field values of under about 650 V/cm.
  • melt is provided by heat-melting a mixture consisting of molybdenum oxide and another oxide selected from the group consisting of gadolinium oxide, europium oxide and terbium oxide, the amount of said molybdenum oxide and said another oxide in said mixture corresponding to the stoichiometric composition of said single crystal.

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US3894142A (en) * 1972-07-28 1975-07-08 Hitachi Ltd Method for producing gadolinium molybdate single crystals having high transparency

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US3500232A (en) * 1966-04-01 1970-03-10 Bell Telephone Labor Inc Solid state laser
US3437432A (en) * 1966-07-21 1969-04-08 Du Pont Single crystals
US3607137A (en) * 1966-11-18 1971-09-21 Hayakawa Denki Kogyo Kk Method of avoiding strain in phase transitions of single crystals
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DE2405912C3 (de) 1978-08-17
DE2405912B2 (de) 1977-08-25
US3993534A (en) 1976-11-23

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