Thermal expansion behaviour of M′Ti2P3O12 (M′=Li,Na, K,Cs) and M″Ti4P6O24 (M″=Mg,Ca, Sr,Ba) compounds

The [NZP] family has been attracting considerable attention because of its potential in thermal shock-resistant applications. The compounds MTi₂P₃O₁₂ (M=Li, Na, K, Cs) and MTi₄P₆O₂₄ (M=Mg, Ca, Sr, Ba) belong to this new family of low-expansion materials. The results of a systematic study undertaken to investigate the thermal expansion behaviour of these materials are reported. A correlation between the ionic size and lattice expansion was also attempted, and compounds possessing lowest bulk thermal and low anisotropy were identified.     

Microstructure and microcracking behaviour of barium zirconium phosphate (BaZr4P6O24) ceramics

Barium zirconium phosphate (BaZr₄P₆O₂₄), a member of a new family of low-thermal-expansion materials known as NZP, was synthesized by the solution sol-gel method, and sintered ceramics were prepared at 1100–1600 °C. The effect of sintering parameters such as time and temperature on the microstructure and phase composition was studied. BaZr₄P₆O₂₄ is known to possess anisotropy in its axial thermal expansions, which usually causes microcracking in the sintered bodies when cooled. The microcracking activity of the sintered samples was examined by acoustic emission measurements.     

New [NZP] materials for protection coatings. Tailoring of thermal expansion

[NZP] (the NaZr₂P₃O₁₂-Family) materials can be selected for synthesizing new thermal shock resistant ceramic coatings with a thermal expansion that can be tailored to match that of the substrate, and to possess a low thermal expansion anisotropy. The tailoring technique will involve the selection of a suitable pair of compositions which, upon being mixed to form a crystalline solution, will possess the desired thermal expansion coefficient and will have negligible thermal expansion anisotropy. This can be done when the axial thermal expansion for one end member is larger in the a-direction than in the c-direction and vice versa for the other end member.     

Synthesis, microstructure and thermal expansion studies on Ca0·5+x/2Sr0·5+x/2Zr4P6−2x Si2x O24 system prepared by co-precipitation method

We report on the synthesis, microstructure and thermal expansion studies on Ca_0·5?+?x/2Sr_0·5?+?x/2Zr₄P_6???2x Si_2x O₂₄ (x = 0·00 to 1·00) system which belongs to NZP family of low thermal expansion ceramics. The ceramics synthesized by co-precipitation method at lower calcination and the sintering temperatures were in pure NZP phase up to x = 0·37. For x ≥ 0·5, in addition to NZP phase, ZrSiO₄ and Ca₂P₂O₇ form as secondary phases after sintering. The bulk thermal expansion behaviour of the members of this system was studied from 30 to 850 °C. The thermal expansion coefficient increases from a negative value to a positive value with the silicon substitution in place of phosphorous and a near zero thermal expansion was observed at x = 0·75. The amount of hysteresis between heating and cooling curves increases progressively from x = 0·00 to 0·37 and then decreases for x > 0·37. The results were analysed on the basis of formation of the silicon based glassy phase and increase in thermal expansion anisotropy with silicon substitution.     

NZP族磷酸盐材料研究进展

NZP族精细磷酸盐材料是一类具有相同晶体结构特征但化学组成各异的结晶化合物粉体及其陶瓷烧结体。综述了NZP族磷酸盐化合物的晶体结构特征、合成方法、NZP族陶瓷的快离子导电性、离子取代性、低热膨胀特性及其应用领域。介绍了NZP族磷酸盐材料作为抗热震催化剂载体和新型介孔分子筛催化剂的研究进展。     

Thermal expansion studies on the Sodium Zirconium Phosphate family of compounds A1/2M2 (PO4)3: effect of interstitial and framework cations

Thermal expansion of the sodium zirconium phosphate (NZP) family of compounds A_1/2M₂(PO₄)₃ (A = Ca or Sr; M = Ti, Zr, Hf or Sn) has been measured in the temperature range 298–1273 K by high-temperature X-ray powder diffractometry. Some of the compounds in the series (calcium zirconium phosphate and calcium hafnium phosphate) display the typical thermal expansion behaviour of NZP compounds, namely expansion along the hexagonal c axis and contraction along the a axis. The other compounds, depending on their interstitial and framework composition, behave differently. The observed axial thermal expansion and contraction behaviour is explained on the basis of the crystal chemistry of the compounds. Low-expansion compounds in this series are identified and their expansion anisotropy examined. Infared spectra of the compounds are reported. Differential scanning calorimetry measurements on the tin compounds indicate the occurrence of a diffuse phase transformation at high temperatures.     

Synthesis,sintering and thermal expansion of Ca1-x Sr x Zr4P6O24 — an ultra-low thermal expansion ceramic system

Ca_1-x Sr _x Zr₄P₆O₂₄ (O × 1.0) system which belongs to a new large family of low thermal expansion materials known as NZP or CTP, was synthesized by the solid state and the sol-gel methods. The conventional sol-gel method was modified by introducing a seeding step which resulted in significant improvement in the sintering characteristics and the microstructure of the sintered material. Sintering data were compared with those obtained by the powder mixing technique. Thermal expansion of the sintered samples was measured by classical dilatometry and by high-temperature X-ray diffractometry. It was found that CaZr₄P₆O₂₄ (x= 0) and SrZr₄P₆O₂₄ (x= 1) phases had opposite anisotropies in their respective axial thermal expansions. This behaviour led to the development of a crystalline solution composition of nearly zero expansion characteristic. Microstructures of the sintered specimens were examined by scanning electron microscopy.     

Strong anisotropic thermal expansion in oxides

The strong anisotropic thermal expansion behavior found for cordierite ((Mg₂Al₄Si₅O₁₅), β-eucryptite (LiAlSiO₄) and NZP (NaZr₂P₃O₁₂) is qualitatively rationalized using distance least squares (DLS) modeling. In this approach, the thermal expansion is driven by the ionic bonds of Mg²⁺, Li⁺ or Na⁺. Due to constraints imposed by shared polyhedra edges or faces, thermal expansion of the ionic bonds expands the lattice in only one or two dimensions. Due to the connectivity in these structures, this expansion in some directions causes contraction in the other directions. The thermal expansion of β-eucryptite was determined from powder neutron diffraction data over the temperature range 10–809 K. This revealed that the volume thermal expansion of β-eucryptite becomes substantially more negative below room temperature than it is above room temperature. The structure was refined by the Rietveld method from data collected at 12 different temperatures. DLS modeling studies suggest that Li–O bond expansion plus movement of Li from tetrahedral to octahedral sites can explain the thermal expansion behavior above room temperature. However, such an approach cannot explain the more pronounced low-temperature negative thermal expansion, which is most likely attributable to rocking motions of AlO₄ and SiO₄ tetrahedra.     

Crystal-Chemical Approach to Predicting the Thermal Expansion of Compounds in the NZP Family

The general structural aspects of phosphates with {[L₂(PO₄)₃] ^p–}₃ frameworks (L = octahedral cation) are considered, and the possible isomorphous substitutions in NaZr₂(PO₄)₃ (NZP) phosphates are analyzed. The available data on the thermal expansion of NZP materials in the range 293–1273 K, together with crystal-chemical data on their structure, are used to identify the processes underlying the thermal expansion of these materials. The results provide basic guidelines in designing NZP-based materials with controlled (ultralow) thermal expansion and near-zero expansion anisotropy.     

Composite route to “zero” expansion ceramics

The use of diphasic or multiphasic composites, involving one negative phase to control and lower the thermal expansion of a ceramic for substrate, laser mirror and anti-thermal shock applications, was studied. The two phases thermodynamically stable with each other — one with negative and the second with positive were mixed, sintered and characterized for thermal expansion behaviour. The negative- phase was selected from the [NZP] or [CTP] structural family. Specific systems including NaZr₂P₃O₁₂, CaZr₄P₆O₂₄ + Nb₂O₅, GdPO₄, ZrSiO₄, Mg₃(PO₄)₂, MgO and ZnO were investigated. Several compositions exhibited a near-zero expansion profile over a wide temperature range.     

Ca1-xBaxZr4(PO4)6磷酸盐陶瓷材料的热膨胀特性

Ca1-xBaxZr4(PO4)6(0≤X≤1.0)属于NZP族磷酸盐陶瓷材料,它是新的一类低热膨胀陶瓷材料。研究发现CaZr(PO4)6(X=0)及BaZr4(PO4)6(X＝1)时的轴膨胀特性正好相反,因此当X为某一值时热膨胀系数将为零。本研究采用共沉淀法合成了Ca1-xBaxZr4(PO4)6磷酸盐陶瓷材料,当X＝0时,热膨胀系数为－0．86×10-61／℃;当X＝0．25时热膨胀系数为2．7×10-61／℃;当X＝0．75时其热膨胀异向性最小。为了得到热膨胀异向性和热膨胀系数均小的Ca1-xBaxZr4(PO4)6磷酸盐陶瓷材料,X应在0．6至0．9之间,并通过控制烧结条件抑制晶粒的生长。     

[NZP]结构功能材料的性能

本文介绍了［ＮＺＰ］陶瓷的各向异性、力学性能、热膨胀行为、抗热震性、离子导电、离子交换、氧化还原和光学等性能，探讨［ＮＺＰ］材料在热负荷环境下的使用和作为隔热材料、固体电解质、抗辐射、催化载体、精密尺寸控制和高温光学窗口材料的应用前景．     

[NZP]陶瓷零膨胀性能的设计

研究了「ＮＺＰ」材料的零膨胀性能，并尝试对零膨胀的「ＮＺＰ」陶瓷作了设计，从晶体结构、原子复合、各向异性、显微结构和复合材料等方面提出了设计思路。     

Negative thermal expansion materials

Materials exhibiting negative thermal expansion through room temperature have a variety of applications, mainly in controlling the overall thermal expansion of various composites. Several materials showing negative thermal expansion have recently been identified. The most dramatic of such behavior is exhibited by ZrW₂O₈, which shows strong isotropic thermal expansion from 20 to 425K.     

Thermal expansion behaviour of barium and strontium zirconium phosphates

Ba_1.5-xSr_xZr₄P₅SiO₂₄ compounds withx = 0, 0.25, 0.5, 0.75, 1.0, 1.25 and 1.5, belonging to the low thermal expansion NZP family were synthesized by the solid state reaction method. The XRD pattern could be completely indexed with respect to space group indicating the ordering of vacancy at the divalent cation octahedral sites. The microstructure and bulk thermal expansion coefficient from room temperature to 800°C of the sintered samples have been studied. All the samples show very low coefficient of thermal expansion (CTE), withx = 0 samples showing negative expansion. A small substitution of strontium in the pure barium compound changes the sign of CTE. Similarly,x = 1.5 sample (pure strontium) shows a positive CTE and a small substitution of barium changes its sign.X = 1.0 and 1.25 samples have almost constant CTE over the entire temperature range. The low thermal expansion of these samples can be attributed to the ordering of the ions in the crystal structure of these materials     

Thermal expansion of NASICON materials

Our and others’ results on the thermal expansion of compounds and the crystal-chemical information about their structure have been used to properly select compositions of new NASICON materials with small thermal expansion and low thermal expansion anisotropy: M _x M_1?x ′Ti₂(PO₄)₃ (M and M′ are alkali metals, 0 ≤ x ≤ 1), M″FeTi(PO₄)₃ (M″ is an alkaline-earth metal), and Ca_{0.5(1 + x)}Fe _x Ti_{2 ? x} (PO₄)₃ (0 ≤ x ≤ 1). Such materials have been synthesized through salt coprecipitation from aqueous solutions and their thermal expansion has been assessed by high-temperature X-ray diffraction. We have determined their unit-cell parameters as functions of temperature and correlated their thermal expansion parameters and composition. The K_0.5Rb_0.5Ti₂(PO₄)₃ and Rb_0.8Cs_0.2Ti₂(PO₄)₃ materials obtained combine small volumetric thermal expansion and near-zero thermal expansion anisotropy.     

Immobilization of lanthanum,cerium, and selenium into ceramic matrix of sodium zirconium phosphate

The crystallographic nature of NaCe_0.2Zr_1.8P₃O₁₂, NaSe_0.2Zr_1.8P₃O₁₂, and NaLa_0.13Ce_0.14Se_0.15·Zr_1.58P₃O₁₂ phases has been investigated with the aim of developing methods for radionuclide immobilization into sodium zirconium phosphate (NZP) phase. The phases have the NZP structure, space group \(R\bar 3c\) , Z = 6. Powder diffraction data have been subjected to Rietveld refinement, and satisfactory structural convergence of R-factors was achieved. The PO₄ stretching and bending vibration bands in the IR region have been assigned.     

Influence of transition metal oxide additions on the crystallization kinetics,microstructures and thermal expansion characteristics of a lithium zinc silicate glass

Lithium zinc silicate glasses can be used to prepare moderately high thermal expansion glass-ceramics, and these materials are ideally suited for the manufacture of hermetic seals to both nickel-based superalloys and stainless steel. On the basis of earlier work by the present authors, one particular composition from the lithium zinc silicate system was chosen for detailed investigation. This composition contains Na₂O and B₂O₃ fluxing agents, together with P₂O₅ as the primary nucleating agent. The crystallization kinetics and resultant microstructures of this composition have been studied as a function of the heat-treatment parameters using differential thermal analysis, dynamic mechanical thermal analysis, scanning and transmission electron microscopy, ambient and high-temperature X-ray diffraction, and small-angle neutron scattering. Indirect evidence from the dynamic mechanical thermal analysis and small-angle neutron scattering suggests that the nucleated glass is phase separated on a very fine scale, of the order of 16 nm. A number of crystalline phases have been positively identified in the heat-treated glasses, including cristobalite, quartz, tridymite, ₁-Li₂ZnSiO₄ and _o-Li₂ZnSiO₄, the precise phases that are formed depending strongly on the heat-treatment parameters. The influence of a number of transition metal oxide additions on the resultant properties of the lithium zinc silicate composition has also been investigated, and it has been shown that the crystallization kinetics, microstructures and thermal expansion characteristics are all strongly affected by these additions. In particular, the activation energy for crystallization (which is related to the nucleating efficiency) is dependent on the ionic field strength of the transition metal ion species employed, with crystallization being favoured by solutes of high field strength.     

Erbium zirconium phosphate Er<Subscript>0.33</Subscript>Zr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> of the NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> family. Structure contraction on heating

Erbium zirconium phosphate Er_0.33Zr₂(PO₄)₃, a member of the family of structural analogs of NaZr₂(PO₄)₃ (NZP), was prepared by the sol-gel process and studied by X-ray phase analysis, IR spectroscopy, and differential scanning calorimetry. The behavior of erbium zirconium phosphate on heating in the temperature interval from 25 to 625°C was studied by high-temperature X-ray diffraction. Expansion and contraction along different crystallographic directions and contraction of the structure as a whole were found. The overall contraction is due to higher contribution of the negative axial thermal expansion coefficients α _a and α _b to α_av and hence to the volume expansion of the phosphate. On heating to 900°C, the NZP structure is preserved.     

Crystal chemistry of the NaZr2(PO4)3, NZP or CTP,structure family

The NaZr₂(PO₄)₃ type structure (abbreviated as NZP or CTP, CaTi₄(PO₄)₆), has emerged as a new family, which has extraordinary technological utility in three fields: fast-ion conductors, radwaste solidification and zero expansion ceramics. NZP or CTP is formed by an extraordinary range of discrete compositions and crystalline solutions. In this paper these compositions are classified according to their crystal chemical substitution scheme, and some uncommon trends in the systematic variation of their lattice parameters are shown. Some of the major trends are explained by correlation with the rotation of polyhedra in the structure.