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Crystal-oriented (Li, Na, K) NbO3 ceramics (LNKN) were prepared by colloidal processing under a strong magnetic field, sintering, and subsequent electrical poling. The [001] direction of the LNKN particles with a tetragonal phase was oriented parallel to the magnetic field. By changing the direction of the magnetic field and machining, [001]-, [100]- and [110]-, and [101]-oriented LNKN powder compacts were formed. After phase transition during sintering, the crystal reorientation was furthermore enhanced by domain switching under an electric field. The obtained [001]-, [001]- and [101]-, and [101]-oriented LNKN ceramics showed piezoelectric constants d31 and d33 of 65 and 120 pm/V, 96 and 165 pm/V, 108 and 180 pm/V, respectively. In addition, d31 and d33 increased in the order of the [001]-, [001]- and [101]-, and [101]- oriented LNKN ceramics, indicating that the [101] orientation caused by domain switching is more effective for enhancing the piezoelectric properties compared to crystal orientation to the c-axis direction.

Sodium super ionic conductor (NASICON)-type Na3Zr2Si2PO12 (NZSP) with the advantages of the high ionic conductivity, stability and safety is one of the most famous solid-state electrolytes. NZSP, however, requires the high sintering temperature about 1200 °C and long sintering time in the conventional solid-state reaction (SSR) method. In this study, the liquid-phase sintering (LPS) method was applied to synthesize NZSP with the use of NaPO3 glass with a low glass transition temperature of 292 °C. The formation of NZSP was confirmed by X-ray diffraction analyses in the samples obtained by the LPS method for the mixture of Na2ZrSi2O7, ZrO2, and NaPO3 glass. The sample sintered at 1000 °C for 10 h exhibited a higher Na+ ion conductivity of 1.81 mS/cm at 100 °C and a lower activation energy of 0.18 eV compared with the samples prepared by the SSR method. It is proposed that a new LPE method is effective for the synthesis of NZSP and the NaPO3 glass has a great contribution to the Na+ diffusion at the grain boundaries.

There has been a great progress in the spatially selected patterning of crystals with a single crystal-like architecture by continuous wave (CW) and femtosecond (fs) pulsed laser irradiations in oxide glasses. Highly oriented crystals with different morphologies such as straight/bending/spiral lines and two-dimensional planar shapes are patterned using heat-driven type CW laser irradiations with a scanning mode. The features of the laser patterning of nonlinear optical crystals with birefringence such as β-BaB2O4, LaBGeO5, LiNbO3, and BaAlBO3F2 are focused, and the origin and mechanism of the c-axis orientation along the laser scanning direction are discussed from the viewpoints of surface energy and interfacial free energy between crystal and surrounding glassy phase. The homo-epitaxial crystal growth in the laser patterning of crystal lines and the rotation of crystal axes in ferroelastic β′-Gd2(MoO4)3 are demonstrated as unique features of the laser-induced crystallization. The laser-induced crystallization provides a new insight and more deep understanding for the nucleation and crystal growth in glasses and proposes a new crystal growth science and engineering in solid-state materials.

The crystallization behavior of sodium ion conductive Na2MnP2O7 glass was examined to clarify the crystallization mechanism. The formation of thermodynamically metastable phase, layered Na2MnP2O7, at the surface of the glass occurred. Heat treatment at 430 °C for 3 h lead to surface crystals of Na2MnP2O7 oriented with the (101) direction perpendicular to the sample surface. As the heat treatment temperature increased, the glass-ceramic samples deformed, and the presence numerous micro bubbles due to dissolved water was detected.

Although the sodium phosphate cathode active materials based on the Ni3+/Ni2+ redox reaction are expected to develop a high discharge potential, none of the studies aimed at practical application have been reported due to its poor kinetics showed in the sodium phosphate. Herein, we substituted active Fe for a part of Ni, expecting to activate the potential deriving from the Ni3+/2+ in Na2FexNi1−xP2O7 glass-ceramics. Precursor glasses were prepared by the melt-quenching method and exhibited surface crystallization tendency due to heterogeneous nucleation. In the charge-discharge testing, all the flat potential showed in the discharge process derived from the reduction of Fe3+/2+. However, from the dQ/dV plot, there were two weak reduction peaks at 4.3 and 4.4 V in the discharge process of Na2Fe0.25Ni0.75P2O7. Combining with the oxidation peak at 4.6 V in the second charge process of Na2NiP2O7, we believe the reduction peaks at 4.3 and 4.4 V were derived from the Ni3+/2+.

Phase separation of amorphized sodium tin silicate and the reduction of tin oxide by heat treatment in hydrogen were characterized. An amorphous powder was prepared by planetary ball milling of a mixture of SnO and sodium disilicate glass (Na2O–2SiO2). xSnO-(100-x)/3Na2O-2 (100-x)/3SiO2 system with x composition less than 55 was confirmed to be amorphous. The amorphous powder was heat-treated in H2/N2 mixture gas and SnO nanocrystals and SnO2 nanocrystals were formed at temperatures up to 360 °C. The reduction of tin oxide to metallic Sn started above 450 °C, and the percentage of metal tin precipitated increased as the heat treatment time increase. We conducted a charge-discharge test in a sodium cell using composite ceramics and succeeded in reducing the irreversible capacity that occurs on the first charge. Sodium tin silicate is a promising anode active material for oxide all-solid-state sodium-ion batteries.

Crystallization behavior of Na2FeyMn1 − -yP2O7 glass prepared by conventional melt-quenching method was examined. And its electrical conductivity and electrochemical properties are also examined. Less than y = 0.25 layered type triclinic phase formed as main phase by heat-treatment at crystallization temperature. The other composition triclinic β phase mainly precipitated. By further heat-treatment up to 650 °C, crystalline phase completely transformed to beta phase in all composition. For the reversible discharge capacity of Na2FeyMn1 − yP2O7 increased by increase of the FeO substitution in both glassy state and glass-ceramics. It is found that Mn3 +/Mn2 + redox reaction in Na2Fe0.25Mn0.75P2O7 glass-ceramic cathode is activated and higher voltage plateau appeared at 3.8 V.

Glasses with compositions of 21Gd2O3-63MoO3-(16-x)B2O3-xTeO2 (mol%) (x = 0, 2, 4, 8) were prepared using a conventional melt quenching technique, and the crystallization behavior of ferroelastic β′-Gd2(MoO4)3 crystals was examined to clarify the mechanism of self-powdering phenomenon and to design bulk crystallized glasses. It was found that the self-powdering phenomenon appeared significantly during the crystallization at temperatures near the crystallization peak temperature, but the phenomenon is suppressed in the crystallization at temperatures much higher than the glass transition temperature. It was also found that the substitution of TeO2 for B2O3 in the base glasses suppresses the self-powdering phenomenon and consequently bulk crystallized glasses were obtained in the glass with x = 8 mol%. The densities at room temperature of the base glasses are d = 4.755–4.906 g/cm3, being much higher than the value of d = 4.555 g/cm3 for β′-Gd2(MoO4)3 crystal. It is proposed that the stresses in the inside of crystals induced by large density differences (i.e., large molar volume differences) between the glassy phase and crystals might be relaxed effectively in the glasses containing TeO2 with weak Te O bonds and fragile character.

The crystallization behavior of ferroelastic β′-Gd2(MoO4)3 with the molar ratio of Gd2O3/MoO3 = 1/3 and Gd4Mo7O27 with Gd2O3/MoO3 = 1/3.5 in Gd2O3-MoO3-B2O3 glasses was studied to clarify the formation mechanism of β′-Gd2(MoO4)3 and the self-powdering phenomenon induced during the crystallization more deeply. In 20Gd2O3-60MoO3-20B2O3 glass, the Gd4Mo7O27 crystalline phase was formed initially in heat-treatments at near the glass transition temperature (Tg = 516 °C) prior to the formation of the β’-Gd2(MoO4)3 crystalline phase at near the crystallization peak temperature (Tp = 583 °C). In 18.89Gd2O3-66.11MoO3-15B2O3-1Al2O3 glass (Tg = 507 °C and Tp = 572 °C) with Gd2O3/MoO3 = 1/3.5, Gd4Mo7O27 crystals were formed through the crystallization and present stably in the wide temperature range and transformed into β'-Gd2(MoO4)3 crystals at a high temperature of 900 °C, proposing new glass-ceramics consisting of Gd4Mo7O27 crystals. The self-powdering phenomenon was not observed in the crystallized glasses with Gd4Mo7O27.

New Eu3+-doped Gd4Mo7O27 crystals (the molar ratio of Gd2O3/MoO3 = 1/3.5) with a monoclinic structure C2/c (an inversion symmetry) were synthesized through the crystallization of xEu2O3-(18.89-x)Gd2O3-66.11MoO3-15B2O3-1Al2O3 glasses (x = 0.0472 and 1.889) and photoluminescence (PL) emissions of Eu3+ ions were measured for the first time. The crystallized glass with no Eu2O3 addition (x = 0) showed a blue color under the irradiation of ultra-violet light with a wavelength of λ = 254 nm, the emitting color of the crystallized glass with x = 0.0472 was pink, and that of the crystallized glass with x = 1.889 was orange. The charge transfer (CT) of O2-→Mo6+ providing broad peaks centered at around 325 nm was observed in the crystallized glasses. The peak intensity at 591 nm for the 5D0→7F1 transition of Eu3+ ions in the crystallized glasses with x = 0.0472 and 1.889 was very close to that at 615 nm for the 5D0→7F2 transition for the excitation of λex = 394.5 nm. We propose potential of Gd4Mo7O27 as a new host crystal for rare-earth-doped phosphors.

Maricite NaFePO4 crystal is expected to be an active cathode material for sodium-ion batteries (SIBs) because of its high theoretical capacity of 155 mAhg−1. NaFePO4 crystal is, however, inactive as a cathode material due to the absence of Na+ ion conduction pathways. A continuous-wave Yb:YVO4 fiber laser (the wavelength of λ = 1080 nm) was irradiated onto NaFePO4 crystal in order to modify its structure and to enhance Na+ ion conductivity. The vitrification of NaFePO4 crystals by laser irradiations was clarified from differential scanning calorimetry (DSC), differential thermal analysis (DTA), X-ray diffraction (XRD), and Raman scattering spectrum analyses. The discharge capacity in the first cycle is 40 mAhg−1 for the rate of 0.01 C, suggesting the development of three-dimensional conduction pathways for Na+ ions by vitrification.

The crystallization behavior of 25Na2O–50WO3–25TeO2 glass was examined to develop transparent glass-ceramics containing nonlinear optical Na2TeW2O9 crystals. It was clarified from XRD analysis and Raman scattering spectra that a metastable crystalline phase is formed initially and the stable crystalline phase of Na2TeW2O9 is created through the transformation of the metastable phase. Laser irradiations (continuous wave Yb:YVO4 fiber laser, wavelength of 1080 nm) with the condition of the laser power of P = 0.55 W and scanning speed of S = 2.3 μm/s created the patterning of homogeneous crystals lines. The crystalline phase in the laser irradiated part was proposed to be the metastable crystalline phase from micro-Raman scattering spectra.

In this study, the short- and medium-range ordering of 21.25Gd

The effect of the substitution of RE2O3 (5 mol%) (RE: Eu, Gd, Er) for Bi2O3 on the thermal stability and crystallization behavior in 33.3Bi2O3-33.3ZnO-33.3B2O3 glass with a low temperature melting feature was clarified to explore new potentials of Bi2O3-based glasses and glass-ceramics. Both the glass transition and crystallization temperatures increased with the RE2O3 addition and the thermal stability against crystallization was enhanced. This is due to the increase in the average chemical bond strength of the glasses with the addition of RE2O3. The formation of RE3+-doped nonlinear optical RExBi2-xZnB2O7 crystals was confirmed from X-ray diffraction analyses and photoluminescence spectra in the glass crystallization. RE2O3 oxides added to the glass do not act as nucleating agents for the crystallization of Bi2ZnB2O7. The photoluminescence related to the 4f-4f transitions of Eu3+ and Er3+ was clearly observed even in the glasses with a relatively large amount (33.3 mol%) of B2O3, suggesting that RE3+ ions are present in the environment of Bi2O3-rich region with low phonon energies.

In order to clarify the possibility of cathode activity of Na 2 O-FeO-P 2 O 5 glasses for sodium ion batteries, glass formation tendency, crystallization behavior, electrical conductivity as well as charge and discharge properties are examined. Glass formation in x FeO–(100- x )NaPO 3 was confirmed for x ≤ 45 by melt quenching up to 1000 °C in N 2 filled electric furnace. By means of electrical conductivity tests, conductivity was increased with increases of x content in x FeO–(100- x )NaPO 3 and the activation energy for electrical conductivity was decreased. Charge and discharge profiles for Na anode exhibits high reversible discharge capacity as 115 mAh/g at 0.1 °C rate in 40FeO-60NaPO 3 (30Na 2 O–40FeO–30P 2 O 5 ) glass. The results on Raman scattering spectra suggests that glass structure is subjected to polymerized Q 1 and Q 2 phosphate units. And polymerized phosphates in glass cause lower density, open structure and sodium ion diffusive channels as well.

High temperature phase of hexagonal SrAl 2 O 4 :Eu 2+ ,Dy 3+ crystals were synthesized via two paths; (1) heat-treatment on glass (a conventional glass crystallization technique), and (2) solidification of supercooled melts in melt-cooling process with non-contact process, where a levitation melting technique was used to obtain precursor glass and ceramics beads. Hexagonal SrAl 2 O 4 (βʹ-phase) were formed in both samples, not stable phase of monoclinic phase (α-phase), which is well known as one of the best afterglow material. Both samples with hexagonal phase showed brighter broad green emission, higher intensity of PLE peak in visible region (λ=400–500 nm), and longer duration of afterglow compared to monoclinic SrAl 2 O 4 :Eu 2+ ,Dy 3+ sintered by solid-state reaction.

Lithium iron silicate glasses with different fractions of Fe 2 + ions of 40Li 2 O–10Fe 2 O 3 –50SiO 2 (mol%) are prepared by conventional melt-quenching method and reducing heat treatment technique, and their electrochemical properties as cathode materials for Li + ion secondary batteries (LIBs: lithium ion batteries) are examined. It is demonstrated for the first time that Li 2 O–Fe 2 O 3 –SiO 2 glasses work as cathode in LIBs, e.g., the discharge capacity at 100/C in the first cycle is 54.6 mAh g − 1 . The heat treatment at 350 °C in 5% H 2 /Ar induces not only the increase in the fraction of Fe 2 + ions but also the increase in the packing density and the decrease in the electrical conductivity. It is clarified that the discharge capacity of the glasses is largely improved due to the increase in the fraction of Fe 2 + ions. The data on thermal, physical, and discharge properties obtained in 40Li 2 O–10Fe 2 O 3 –50SiO 2 glasses are compared with those in borate and phosphate glasses of 40Li 2 O–10Fe 2 O 3 –50(B 2 O 3 , P 2 O 5 ).

All-solid-state Na-ion batteries (Na-ASSBs) with an oxide solid electrolyte have been successfully developed using crystallized glass as the cathode active material. Melt flow during the crystallization of the precursor glass enables the cathode to be integrated with a solid electrolyte. Such a effectively integrated cathode/solid electrolyte shows excellent battery performance and high cycling stability. All-solid-state batteries with an oxide solid electrolyte are more thermally stable and safer than conventional lithium-ion batteries with an organic liquid electrolyte. In addition, owing to the use of Na, which is abundant natural resources, Na-ASSBs can be manufactured stably without the risk of resource shortage. Therefore, we believe that Na-ASSBs are among the most promising next-generation energy storages with high safety and large capacity. β”-alumina is a common oxide solid electrolyte with high ion conductivity comparable to the organic liquid electrolyte. If β”-alumina can replace organic electrolytes, safer Na-ASSBs operating over a wide temperature range can be fabricated. However, it is difficult to establish effective contact between the cathode material and the oxide solid electrolyte. In this work, we focused on Na-ASSBs using Na2FeP2O7 crystallized glass as the cathode. [1,2] Na2O-Fe2O3-P2O5 precursor glass powder, β”-alumina powder, and acetylene black were mixed to prepare a cathode mixture, which was applied on a β”-alumina substrate, followed by heating to sinter and crystallize the glass. As a result, the solid electrolyte and cathode were successfully integrated. Then, Na metal was attached to the counter side as the anode. The Na-ASSB with such effective integration showed rapid charge/discharge performance (10C) even at room temperature, which in turn enabled the motor to be operated at room temperature (Fig. 1). Furthermore, the cycle performance test at 10C rate and 30°C showed that the capacity retention after 1000 cycles was 94%. The excellent battery performances allow for the practical application of Na-ASSBs. This presentation will focus on the performance of Na-ASSBs and the manner in which it can be realized. References [1] T. Honma et al., J. Ceram. Soc. Jpn. 120 (2012) 344-346. [2] T. Honma et al., J. Power Sources 227 (2013) 31-34. [3] H. Yamauchi et al., J. Am. Ceram. Soc. 102 (2019) 6658-6667. [4] H. Yamauchi et al., (In press). Enhanced rate capabilities in a glass-ceramic-derived sodium all-solid-state battery. Sci. Rep. Figure 1

Understanding of nanoscale heterogeneous structure, in particular composition fluctuations in multi-component oxide glasses, is a great challenge in the science and technology of solid state materials. The data on the crystallization of oxide glasses, especially the relationship between crystalline phases and glass compositions, are reviewed, and the distribution model of composition fluctuations is proposed for the first time. The crystallization data-driven proposal model on composition fluctuations consists of network former-rich (high viscosity) strong region and network modifier-rich (low viscosity) fragile region, and crystallization including the formation of metastable phases is initiated preferentially in the fragile region. Crystallization behaviors such as lithium disilicate Li2Si2O5 crystals in Li2O-2SiO2 glass, LiNbO3 crystals in 40Li2O-32Nb2O5-28SiO2 glass, and ferroelastic β′-Gd2(MoO4)3 crystals in 21.25Gd2O3-63.75MoO3-15B2O3 glass are reviewed as model cases. The proposed model will shed new light on the medium-range order and nanoscale heterogeneous structure in oxide glasses and also will guide to an innovative design of glass compositions leading to new functional glasses and glass-ceramics.