Design Of The Crystal Growth Furnace With Magnetostatic Field And Crystal Growth

Bridgman method is an important way to grow relaxor ferroelectric single crystals with large size.However,due to the gravity of the earth,there is thermal convection in high temperature melt,which makes it difficult to guarantee the stability of boundary layer.Therefore,the crystals grown by Bridgman method have inhomogeneous composition and defects,leading to the low stability of properties.Because the magnetic field can inhibit the convection in the conductive melt,a C-type transverse magnetic field is proposed during the growth of single crystal.On the basis of previous experience,a shrinkage type Bridgman single crystal growth furnace with C-type transverse magnetic field was designed and constructed.In order to explore the optimum the proess parameters of PZN-PT:Nd/Gd and PZN-9PT:Er/Nd single crystal,the high-temperature solution method was used,which could supply the helpful information for the growth of single crystal by Bridgman method in magnetic field.The structure and properties of PZN-9PT single crystals were studied.In order to improve the magnetic field strength effectively,a shrinkage Bridgman single crystal furnace was designed and built.The size of built furnace is 740 mm×500 mm×745 mm,The heater of furnace is silicon molybdenum bars,using 1460 and 1260 refractory fibers,containing zirconium,polycrystalline mullite,alumina hollow sphere brick as the insulation layer and refractory layer of the furnace body.Using this way not only reduce the size of furnace but also guaranteed the thermal performance.Through repetitive heating experiments,it is found that the single crystal furnace can provide a high temperature environment of 0-1400?,which can meet the practical requirements.A C-type DC magnetostatic field device(electromagnet)made of DT4E pure iron core,DT4E pure iron yoke and flat copper wire coil was designed.Based on requirement of the magnetic field intensity of 0.2 T at the gap center of the magnetic pole to suppress convection,the ampere-turn number is 47788 A by calculating the magnetic circuit of the designed electromagnet.ANSYS Maxwell software is used to simulate the relationship between magnetic induction intensity and current and coil turns,and it is found that magnetic induction intensity increases with the increase of current and turns.The distribution of magnetic field between magnetic poles at 47788 A is simulated using Calculator in software,and the magnetic field intensity is 0.17 T at the center of magnetic gap.On the basis of the simulation results and magnetic circuit analysis,the current of 40 A and turn number of 1194 is chosen as the final ampere-turn coordination.The PZN-9PT:Er/Nd and PZN-9PT:Nd/Gd crystals were grown by high temperature solution method and the maximum size reaches 5 mm×4 mm×4 mm.The PZN-9PT:Er/Nd and PZN-9PT:Nd/Gd crystals exhibit high ferroelectric-paraelectric transition temperatures of 174.3? and 165.2?,large remanenent polarization intensities of 23 ?C/cm2 and 40 ?C/cm2 and large coercive fields of 22 kV/cm and 20 kV/cm,respectively.Under an 800 nm laser excitation,both crystals show up-conversion luminescence from near infrared to blue and green light.The M-H loops show that both crystals are paramagnetic.