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The preparations of (K 0.5 Na 0.5 )NbO 3 (KNN)-based ceramics were studied as lead-free piezoelectric materials. The authors found that the addition of CuO greatly enhanced the sinterability of the KNN-based ceramics. The sinterability and piezoelectric properties of these ceramics were dependent upon the A/B ratio, CuO doping, and the formation of a solid solution with KTaO 3 . Perovskite (K 0.5 Na 0.5 ) x NbO 3 (x = A/B ratio) was synthesized with A/B ratios of 1.00 and 1.05 by CuO doping, while (K 0.5 Na 0.5 )NbO 3 contained K 4 CuNb 8 O 23 as a second phase with A/B ratios below 0.98. Although the A site-rich (K 0.5 Na 0.5 )NbO 3 (x = 1.00 and 1.05) ceramics exhibited deliquescence, the A site-poor (K 0.5 Na 0.5 )NbO 3 (x ≤ 0.98) ceramics with K 4 CuNb 8 O 23 had higher densities without deliquescence. K 4 CuNb 8 O 23 also improved Q m , which reached 1400 for the (K 0.5 Na 0.5 ) 1.0 NbO 3 doped with 0.5 mol% K 4 CuNb 8 O 23 . The formation of a solid solution with KTaO 3 raised the melting point of the system and also improved its sinterability. The k p and Q m of (K 0.5 Na 0.5 ) 0.97 (Nb 0.95 Ta 0.05 )O 3 with CuO were 0.41 and 1400, respectively.

Transparent and highly oriented K x (Sr 0.5 Ba 0.5 ) 1-x/2 Nb 2 O (x = 0.2, 0.4) (KSBN) thin films have been synthesized by a chemical solution deposition method. A homogeneous and stable KSBN precursor solution was prepared by controlling the reaction of metallo-organics. K 0.4 Sr 0.4 Ba 0.4 Nb 2 O 6 (x = 0.4, K 0.4 SBN50) and K 0.2 Sr 0.45 Ba 0.45 Nb 2 O 6 (x = 0.2, K 0.2 SBN50) powders and thin films directly crystallized to the tetragonal tungsten bronze phase above 600°C. The thin films were crystallized on MgO(100) and Pt(100)/ MgO(100) with c-axis preferred orientation. Two crystal lattice planes of K 0.4 SBN50 and K 0.2 SBN50 were intergrown at an orientation of 18.5° on MgO(100) and Pt(100)/ MgO(100). K 0.4 SBN50 thin film on Pt(100)/MgO(100) showed the typical hysteresis loop (P r = 22 μC/cm 2 , E c = 99 kV/cm at -190°C). The change in remnant polarization with temperature is strongly related to the diffuse phase transition of the e-T curves.

Transparent and highly oriented Ba 2 NaNb 5 O 15 (BNN) thin films have been prepared by using metal alkoxides. A homogeneous precursor solution was prepared by the controlled reaction of NaOC 2 H 5 , Nb(OC 2 H 5 ) 5 , and barium metal. The BNN precursor included a molecular-level mixture of NaNb(OC 2 H 5 ) 6 and Ba[Nb(OC 2 H 5 ) 6 ] 2 in ethanol. The alkoxy-derived powder crystallized to a low-temperature phase, and then transformed to orthorhombic BNN (tungsten bronze) at 600°C. BNN precursor films on substrates crystallized to orthorhombic BNN at 800°C via the low-temperature phase. Highly (002) oriented BNN films of tungsten bronze structure were successfully prepared on MgO (100) substrates at 700°C by using BNN underlayer.

Composites consisting of a Ce-TZP matrix and in-situ grown particles of La(Fe,Al)12O19 were prepared by the solid-state reaction of Ce-TZP, La(Fe,Al)O3, and Al2O3 powders. The in-situ formation process of La(Fe,Al)12O19 in a Ce-TZP matrix was investigated in relation to the microstructure evolution. The Ce-TZP-La(Fe,Al)12O19 composites had significant magnetic properties and improved mechanical properties. The maximum value of magnetization of the Ce-TZP-La(Fe,Al)12O19 composites was obtained at 90 mol% LaFe12O19 in La(Fe,Al)12O19. The value of the three-point bending strength of Ce-TZP-20 wt% La(Fe,Al)12O19 (90 mol% LaFe12O19) sintered at 1350°C was 780 MPa, compared with 500 MPa of Ce-TZP ceramics. The composite demonstrated crack sensing based upon the change in magnetic gradient.

Crack-free and dense KTiOPO4 (KTP) fibers could be successfully synthesized through metallo-organics. A homogeneous, drawable KTP precursor solution was prepared from the reaction of (nBuO)2P(O)(OH), Ti(OEt)4, and KOEt. KTP precursor fibers crystallized to a single-phase KTP at 650°C for 0.5 h. KTP fibers were a few centimeters in length and 10–150 μm in diameter. The density of the KTP fibers was higher than 2.97 g/cm3 (>98% of theoretical density).

The gas-sensing properties of spinodally decomposed (Ti,Sn)O2 thin films on sapphire substrates were investigated for CO, C3H8, and C2H5OH, and hydrogen gases at a temperature of 500°C. The variation in the d-spacing of the (101) plane of (Ti0.5Sn0.5)O2 films showed behavior that was typical of spinodal decomposition during annealing at a temperature of 900°C. Transmission electron micrographs of the spinodally decomposed (Ti,Sn)O2 films on sapphire (0112) substrates revealed the characteristic modulated structure. The modulated lamella microstructure consisted of TiO2- and SnO2-rich regions at intervals of ∼10 nm. The films were very sensitive to hydrogen gas and revealed anisotropic electrical conduction that was influenced by the modulated microstructure, which is characteristic of spinodal decomposition.

Ba2NaNb5O15 (BNN) thin films with a tungsten bronze structure were fabricated using a precursor solution that was synthesized from barium, sodium, and niobium alkoxides. Highly (002)-oriented BNN films were prepared successfully on Pt(100)/MgO(100) substrates at 700°C, using a BNN underlayer. X-ray pole-figure measurement showed that the BNN films that crystallized on Pt(100)/MgO(100) substrates had two in-plane orientations. The remanent polarization and coercive field of the BNN film (thickness of 1.0 µm) that was crystallized at 700°C were 12.3 µC/cm2 and 101 kV/cm, respectively, at –150°C (123 K). BNN films on fused silica substrates exhibited second harmonic generation upon irradiation with 1064 nm light.

K(Ta,Nb)O3 (KTN) thin films have been prepared by the chemical solution deposition method. KTN precursors consisted of a uniform mixture of K[Ta(OC2H5)6] and K[Nb(OC2H5)6] with interaction at the molecular level. Perovskite KTN thin films with the desired composition (Ta/Nb = 65/35, 50/50, and 35/65) were synthesized from the precursor solutions by the dip coating method. KTN thin films with (100) preferred orientation were successfully synthesized on MgO(100) and Pt(100)/MgO(100) substrates. X-ray pole figure measurements showed that grains of KTN films had a prominent three-dimensional regularity on MgO(100) and Pt(100)/MgO(100) surfaces. The Curie temperatures of KTN films decreased with increasing Ta/Nb ratio. Typical P-E hysteresis loops were observed for KTN thin films of three compositions on Pt(100)/MgO(100) substrates. The values of remanent polarization (Pr) of KTN films increased as the Ta/Nb ratio changed from 65/35 to 35/65.

The effects of the substitution of transition-metal ions and/or reductant gases on the catalytic properties of barium hexaaluminogallate were investigated. Transition-metal-substituted hexaaluminogallates (BaM(Al,Ga) 11 O 19 , M = transition metal, Al/Ga = 9/3) were synthesized from aqueous metal nitrates and ammonium carbonate by the coprecipitation followed by crystallization at 1100°C. The direct NO x reduction was observed over BaM(Al,Ga) 11 O 19 to be around 10%. The NO x removal activity of BaM(Al,Ga) 11 O 19 powders was improved by addition of C 3 H 6 as a reductant gas. Co-, Ni- and Cu-substituted BaM(Al,Ga) 11 O 19 catalysts exhibited about 40% NO x reduction with C 3 H 6 in excess oxygen at a high space velocity of 10000 h -1 . The NO x reduction on Mn- and Fe-substituted BaM(Al,Ga) 11 O 19 catalysts was less than 10% even in the presence of C 3 H 6 . The temperature of the effective NO x reduction on BaM(Al,Ga) 11 O 19 catalysts could be adjusted from 350° to 500°C by the selection of the transition-metal substitution in the catalysts. The catalysts hold high activities for NO x reduction even at 500°C in water vapor produced in the combustion system of reductant gases.

Barium hexaaluminogallate was synthesized by the mixed-oxide method and the coprecipitation method. Barium hexaaluminate and barium hexagallate were found to form barium hexaaluminogallate, Ba(Al,Ga)12O19, at 1400°C. BaCo(Al,Ga)11O19 of magnetoplumbite structure was formed from a mixture of metal oxides at 1200°C for 6 h. Co was successfully introduced to barium hexaaluminogallate, although the synthesis of BaCoAl11O19 is quite difficult via solid-state reaction of oxide powders. Anisotropic BaCo(Al,Ga)11O19 particles crystallized at 1100°C for 2 h through the coprecipitation method using metal nitrates and ammonium carbonate. BaCo(Al,Ga)11O19 supported on a cordierite honeycomb had the ability to reduce NOx with methane over 500°C in the presence of excess oxygen.

Strontium titanate (SrTiO 3 )-based multilayered film with varistor characteristics has successfully been fabricated by a chemical solution deposition (CSD) method. Homogeneous precursor solutions of SrTiO 3 and Nb:SrTiO 3 with long-term stability could be prepared by optimizing the reaction conditions among strontium ethoxide, titanium isopropoxide, and niobium ethoxide. Films were prepared using the precursor solutions on fused silica substrates at 700°C. Triple layered films with SrTiO 3 /Nb:SrTiO 3 SrTiO 3 structure were also successfully crystallized on Pt/Ti/SiO 2 /Si substrates at 700°C. The current-voltage (I-V) curve of the multilayered film was characteristic to varistors and the nonlinear coefficient a of the synthesized film was ∼3.0. The varistor voltages (E 0.01 ) of 0.6-μm-thick film were 140 kV/cm for the forward direction and -120 kV/cm for the reverse direction, respectively, at room temperature.

Nd: YVO4 powders and thin films were successfuly synthesized by the sol–gel method using metal alkoxides. A homogeneous and stable solution was prepared by the reaction of Y(OEt)3, VO(OiPr)3, and Nd(OEt)3 in 2-methoxyethanol. The precursor was a mixture of vanadium and yttrium double alkoxide. Precursor films were prepared by dip coating and crystallization to single-phase YVO4 at 500°C. Nd:YVO4 films were crystallized with (200) preferred orientation on glass substrates, which showed the characteristic optical absorption of neodymium.

Two processes for the crystallization of titanium-doped LiNbO3 (LNT) gel thin films were investigated in the present study. LNT gel thin films were prepared on platinized glass and platinized sapphire substrates, as the application of a platinum intermediate layer greatly affected the orientation of LNT films on these substrates. X-ray pole figures revealed the well-oriented growth for LiNbO3 both on the platinum (111)/sapphire C substrate and bare sapphire C. Another approach to crystallizing LNT gel film was attempted by developing a new technique to fabricate a LiNbO3 waveguide on the sapphire substrate using a Nd:YAG laser beam. The crystallization of LNT was achieved successfully with no cracking or peeling. The prepared crystalline LNT films also were characterized by Raman microspectroscopy. S. E. Trolier-McKinstry—contributing editor

Crack-free, dense, and transparent Pb0.6Ba0.4Nb2O6 (PBN60) thin films have been prepared by a sol-gel method with metal alkoxides and metal acetate. A homogeneous and stable precursor solution was obtained from Ba metal, Pb(CH3COO)2, and Nb(OEt)5 in 2-methoxyethanol. PBN60 powder crystallized to the hexagonal phase at 600°C and then completely transformed to the orthorhombic phase of the tungsten bronze structure at 1250°C. The hexagonal phase was formed on SiO2 glass, MgO(lOO), and sapphire(R) substrate at 600°C, while the orthorhombic phase was only on a sapphire(C) substrate. Orthorhombic PBN60 films with c-axis preferred orientation were successfully synthesized on sapphire(C) substrates at 600°C.

Crack-free and highly transparent KTiOPO4 (KTP) thin films were synthesized by the sol-gel method using a homogeneous precursor solution prepared from (“BuO)2-P(O)(OH), Ti(OEt)4, and KOEt in EtOH. Precipitated powders from the solution crystallized directly to KTP above 550°C. Polycrystalline KTP thin films were obtained at 600°C on various substrates. On NdAlO3(100) substrates, KTP films with (101) and (240) preferred orientations were formed at 600°C. KTP films on glass substrates showed a refractive index of 1.75 and an absorption edge of 350 nm. KTP films exhibited the second harmonic generation of the 532 nm light on irradiaton with 1064 nm light.

Highly oriented K(Ta,Nb)O3 (Ta:Nb = 65:35) (KTN) thin films of perovskite structure were synthesized successfully on Pt(100)/MgO(100) substrates from a metal alkoxide solution through reaction control. Homogeneous KTN coating solutions prepared from KOC2H5, Ta(OC2H5)5, and Nb(OC2H5)5 in ethanol were analyzed by 1H, 13C, and 93Nb NMR spectroscopy. The KTN precursor included a molecular-level mixture of K[M(OC2H5)6] (M = Ta, Nb) units interacting in ethanol solution. X-ray pole figure measurement showed that perovskite KTN films crystallized on Pt(100)/MgO(100) substrates had not only a (100) orientation but also a three-dimensional regularity of grains. The remanent polarization and coercive field of the KTN film (thickness, 1.0 μm) crystallized at 700°C were 1.5 μC/cm2 and 8.7 kV/cm, respectively, at 225 K.

Patterned lithium niobate (LN) films were synthesized successfully from a precursor film containing 1-phenyl-1,3-butanedione (PBD) by ultraviolet (UV) irradiation. A LN precursor solution composed of lithium ethoxide and niobium ethoxide was modified with PBD in ethanol to form LiNb(OEt)6-n(PBD)n, which was designed to have a specific UV absorption at 330 nm. The precursor film began to crystallize at 400°C on sapphire C substrates. The UV absorption band at 330 nm in the precursor film decreased in intensity with increased exposure time to UV light. The patterned LN films crystallized at 550°C on sapphire C substrates showed a (006) preferred orientation.

(Co,Fe)3O4 films were synthesized by the sol–gel method through metalorganic compounds. The (Co,Fe)3O4 films (Co:Fe = 2:1) showed the characteristic behavior of the spinodal decomposition by heat treatments within the miscibility gap. The coercive force of the spinodally decomposed films increased from 0.9 kOe for a solid solution to 2.0 kOe for films that underwent the spinodal decomposition. The nonmagnetic phase (rich in Co) formed by the spinodal decomposition contributes to the pinning of the movement of magnetic domain walls. On the other hand, the (Co,Fe)3O4 films (Co:Fe = 1:1) showed the typical feature of binodal decomposition during heat treatment within the miscibility gap. The binodally decomposed films showed a slight increase in the coercive force depending upon the evolution of the magnetic region.

This paper reports on crack-free Pb(Zr,Ti)O[sub 3] (PZT) thin films with preferred orientation that were prepared successfully on MgO (100), SrTiO[sub 3] (100), and Pt/Ti/SiO[sub 2]/Si substrates from metal alkoxide solutions. Calcination of precursor films in a H[sub 2]O[minus] O[sub 2] gas mixture was found to be effective not only for low-temperature crystallization of perovskite PZT, but also for obtaining the preferred orientation of PZT films. Single-phase PZT films with high preferred orientation were synthesized on MgO (100) and Pt/Ti/SiO[sub 2]/Si substrates at 550[degrees] and 600[degrees] C for 2 h, respectively. The PZT film on the Pt/Ti/Si-O[sub 2]/Si substrate showed a permittivity of 520, tan [delta] of 0.03, a remanent polarization of 24 [mu]C/cm[sup 2], and a coercive field of 54 kV/cm.

This paper reports on crack-free SBN (Sr{sub x}Ba{sub 1{minus}x}Nb{sub 2}O{sub 6}) thin films that have been prepared by a sol-gel method with metal alkoxides. A homogeneous and stable precursor solution was obtained from Sr and Ba metal and Nb(OEt){sub 5} in ethanol with a key additive of ethoxyethanol. SBN (where x = 0.5) powder crystallized to orthorhombic phase at 700{degrees}C, and then transformed completely to tetragonal phase at 1200{degrees}C. The formation of tetragonal SBN was observed on sapphire (R) substrates at 700{degrees}C, whereas the tetragonal phase began to appear in the powders at 1000{degrees}C. SBN films with highly preferred orientation were successfully synthesized on MgO (100) substrates at 670{degrees}C.

This paper reports on perovskite potassium tantalate niobate (KTN) powders and thin films that were synthesized from a metal alkoxide solution. Homogeneous KTN coating solutions were prepared from KOC{sub 2}H{sub 5}, Ta(OC{sub 2}H{sub 5}){sub 5}, and Nb(OC{sub 2}H{sub 5}){sub 5} in absolute ethanol. The precursor powders crystallized to pyrochlore at {approx}650{degrees}C, and then to perovskite at {approx}750{degrees}C, depending upon Ta:Nb ratio. H{sub 2}O vapor during calcination was found to play a prominent role in the direct and predominant crystallization of perovskite films with preferred orientation. Highly oriented KTN films of perovskite structure were successfully prepared on MgO (100) substrates at 675{degrees}C.

This paper reports cubic BN synthesized under high-temperature and -pressure conditions from BN Powder formed by Pressure pyrolysis of borazine below 700{degrees}C and 100 MPa. The conversion of BN powder to cubic BN was strongly influenced by the residual hydrogen identified by the BH/BN ratio of IR absorption band. The activation energy for cubic BN synthesis from BN powder-20 mol% AIN was 46 kJ/mol, when the starting BN was synthesized at 250{degrees}C. A mixture of BN powder and cubic BN particles was converted to cubic BN in the 100% yield by heat treatment at 1800{degrees}C and 6.5 GPa without any catalyst. The presence of cubic BN particles does enhance the conversion to cubic BN from BN powder. The energy required for the transformation of starting BN to cubic BN in the presence of cubic BN seed was 355 kJ/mol.

β-BaB 2 O 4 (β-BBO) powders and films were successfully synthesized by the sol-gel method using metal alkoxides. A homogeneous and stable solution was prepared by the reacton of barium metal with boron triethoxide in ethanol by addition of diethanolamine. The drip-coated precursor films began to crystallize to β-BBO on Pt substrates at 500 o C and converted to β-BBO films with preferred orientation to the c-axis at 700 o C

Oriented (Ti,Sn)O 2 thin films with modulated microstructure were successfully synthesized on sapphire substrates by using sol-gel processing combined with spinodal decomposition. The degree of orientation of (Ti 0.5 Sn 0.5 )O thin films increased in the following order: sapphire (0001), (1120), and (0112). (Ti 0.5 Sn 0.5 )O 2 thin films underwent spinodal decomposition at 900°C by annealing. The variation of the 2Θ value of the 202 reflection of (Ti 0.5 Sn 0.5 )O 2 films showed the typical behavior of spinodal decomposition. The rate of spinodal decomposition of the (Ti 0.5 Sn 0.5 )O 2 films on sapphire (1120) was faster than that on sapphire (0112) substrates. The characteristic modulated microstructure was observed for the spinodally decomposed (Ti 0.5 Sn 0.5 )O 2 films on sapphire (0112) substrates by transmission electron microscopy. (Ti 0.3 Sn 0.7 )O 2 films on sapphire (0112) substrates were binodally decomposed during annealing at 1300°C.