Barium metaborate (BaB 2O 4) exists in two forms the high temperature for m α phase and the low temperature form β phase,with the phase transition poi nt at around 925℃.The low temperature phase (β BBO) is an exce...Barium metaborate (BaB 2O 4) exists in two forms the high temperature for m α phase and the low temperature form β phase,with the phase transition poi nt at around 925℃.The low temperature phase (β BBO) is an excellent NLO cryst al for UV region,while the high temperature one (α BBO) is known as a good bir efringent material.α BBO crystal possesses better transparency in the ultravio let region compared with commonly used YVO 4 and CaCO 3 crystals.However,due t o phase transition problem,it is difficult to grow single α BBO crystals by D CZ method,which restricts its wider application.α BBO crystal usually cracks upon cooling resulted from phase transition to β phase.Therefore,it is difficult to grow β BBO single crystals directly from pure BaB 2O 4 mel t;however,to grow single crystals of α BBO is not easy,either. Our recent experiments showed that one could avoid cracking of α BBO cryst als by Sr 2+ doping.This minute amount of Sr 2+ plays the role of structure stabilizer,which inhibits structural reconstruction. In this way,Sr 2+ d op ed BBO single crystals do not subject to phase transition from 925℃ down to roo m temperature. We have mow successfully grown out α BBO single crystals 30mm in diameter by D CZ method from Sr x Ba 1- x BO 4 melt with Sr concentration 0.3 0 .5%.The ratation rate is 10 15r/min,pulling speed is 1 2mm/h.Preliminary tests revealed that its structure and physic chemical properties were almost identic al to those grown from pure melts.These Sr 2+ doped α BBO crystals are no w being widely used in optical isolators.展开更多
Liquid crystalline of a new carbosilane dendrimer of the second generation(D2) containing thirty-six 4-nitroazobenzene groups in its periphery was characterized by means of polarizing optical micrograph, DSC and WAXD....Liquid crystalline of a new carbosilane dendrimer of the second generation(D2) containing thirty-six 4-nitroazobenzene groups in its periphery was characterized by means of polarizing optical micrograph, DSC and WAXD. Mesogenic compound M5 exhibits threaded, schlieren and inversion lines texture of the nematic phase on the cooling from isotropic phase to solidified temperature. Dendrimer D2 shows the focal conic fan-shaped texture of the smectic A phase on the heating course from 69 to 187 ℃ and on the cooling course from 183 to 64 ℃. After cooling, the smectic E(S E) phase with a texture of the focal conic fan-shape with stripes and concentric arcs appears from smectic A(S A) phase. Phase behavior of dendrimer D2 in liquid crystalline state was K69S A187I182S A57S E47K. The isotropic-smectic A transition enthalpy, smectic A-smectic E transition enthalpy and isotropic-smectic A transition entropy were 1.8, 4.5 and 4.0 J/(K·mol), respectively, and were in agreement with or close to those of small molecular liquid crystal.展开更多
PhCH2)3Sn·(O2CC5H4N)·(H2O)]n was synthesized by the reaction of 4-pyridine car-boxylic acid with the tribenzyltin o xide and was characterized by IR,1 H NMR and MS.Its crystal structure was determined by X-r...PhCH2)3Sn·(O2CC5H4N)·(H2O)]n was synthesized by the reaction of 4-pyridine car-boxylic acid with the tribenzyltin o xide and was characterized by IR,1 H NMR and MS.Its crystal structure was determined by X-ray single crystal diffraction.The crystal belongs to monoclinic.The space group P21 /c with unit cell parameters a=1.2241(8)nm,b=0.9660(6)nm,c=2.3708(15)nm,β=102.722(12)°,V=2.734(3)nm3,Z =4,Dc=1.298g·cm-3 .In crystal,the tin atom rendered five-coordinate in a trigo nal bipyramidal structure which is b ridged by 4-pyridine carboxy-late into one-dimensional chain polymers.展开更多
文摘Barium metaborate (BaB 2O 4) exists in two forms the high temperature for m α phase and the low temperature form β phase,with the phase transition poi nt at around 925℃.The low temperature phase (β BBO) is an excellent NLO cryst al for UV region,while the high temperature one (α BBO) is known as a good bir efringent material.α BBO crystal possesses better transparency in the ultravio let region compared with commonly used YVO 4 and CaCO 3 crystals.However,due t o phase transition problem,it is difficult to grow single α BBO crystals by D CZ method,which restricts its wider application.α BBO crystal usually cracks upon cooling resulted from phase transition to β phase.Therefore,it is difficult to grow β BBO single crystals directly from pure BaB 2O 4 mel t;however,to grow single crystals of α BBO is not easy,either. Our recent experiments showed that one could avoid cracking of α BBO cryst als by Sr 2+ doping.This minute amount of Sr 2+ plays the role of structure stabilizer,which inhibits structural reconstruction. In this way,Sr 2+ d op ed BBO single crystals do not subject to phase transition from 925℃ down to roo m temperature. We have mow successfully grown out α BBO single crystals 30mm in diameter by D CZ method from Sr x Ba 1- x BO 4 melt with Sr concentration 0.3 0 .5%.The ratation rate is 10 15r/min,pulling speed is 1 2mm/h.Preliminary tests revealed that its structure and physic chemical properties were almost identic al to those grown from pure melts.These Sr 2+ doped α BBO crystals are no w being widely used in optical isolators.
文摘Liquid crystalline of a new carbosilane dendrimer of the second generation(D2) containing thirty-six 4-nitroazobenzene groups in its periphery was characterized by means of polarizing optical micrograph, DSC and WAXD. Mesogenic compound M5 exhibits threaded, schlieren and inversion lines texture of the nematic phase on the cooling from isotropic phase to solidified temperature. Dendrimer D2 shows the focal conic fan-shaped texture of the smectic A phase on the heating course from 69 to 187 ℃ and on the cooling course from 183 to 64 ℃. After cooling, the smectic E(S E) phase with a texture of the focal conic fan-shape with stripes and concentric arcs appears from smectic A(S A) phase. Phase behavior of dendrimer D2 in liquid crystalline state was K69S A187I182S A57S E47K. The isotropic-smectic A transition enthalpy, smectic A-smectic E transition enthalpy and isotropic-smectic A transition entropy were 1.8, 4.5 and 4.0 J/(K·mol), respectively, and were in agreement with or close to those of small molecular liquid crystal.
文摘PhCH2)3Sn·(O2CC5H4N)·(H2O)]n was synthesized by the reaction of 4-pyridine car-boxylic acid with the tribenzyltin o xide and was characterized by IR,1 H NMR and MS.Its crystal structure was determined by X-ray single crystal diffraction.The crystal belongs to monoclinic.The space group P21 /c with unit cell parameters a=1.2241(8)nm,b=0.9660(6)nm,c=2.3708(15)nm,β=102.722(12)°,V=2.734(3)nm3,Z =4,Dc=1.298g·cm-3 .In crystal,the tin atom rendered five-coordinate in a trigo nal bipyramidal structure which is b ridged by 4-pyridine carboxy-late into one-dimensional chain polymers.
