Materials and Design 31 (2010) 3353–3357

Contents lists available at ScienceDirect

Materials and Design

journal homepage: www.elsevier .com/locate /matdes

Influence of dysprosium oxide doping on thermophysical propertiesof LaMgAl11O19 ceramics

Yuan-Hong Wang, Jia-Hu Ouyang *, Zhan-Guo LiuInstitute for Advanced Ceramics, Department of Materials Science, Harbin Institute of Technology, No. 92, West Da-Zhi Street, Harbin 150001, PR China

a r t i c l e i n f o a b s t r a c t

Article history:Received 5 December 2009Accepted 30 January 2010Available online 6 February 2010

Keywords:LaMgAl11O19

Dy2O3 dopingThermal conductivityThermal expansion

0261-3069/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.matdes.2010.01.058

* Corresponding author. Tel./fax: +86 451 8641429E-mail address: ouyangjh@hit.edu.cn (J.-H. Ouyang

This paper deals with the influence of dysprosium oxide doping on thermophysical properties of LaM-gAl11O19 ceramics. LaMgAl11O19 ceramic powders doped with different contents of dysprosium oxidewere pressureless-sintered at 1700 �C for 10 h in air to fabricate dense bulk ceramics. La1�xDyxMgAl11O19

(x = 0, 0.1, 0.2, 0.3) ceramics have a relative density of 90.7–96.0%, and exhibit a single phase of magne-toplumbite structure. Thermal diffusivity and thermal expansion coefficients of La1�xDyxMgAl11O19

ceramics were measured with a laser flash method and a high-temperature dilatometer. Thermal diffu-sivity of La1�xDyxMgAl11O19 ceramics decreases with increasing Dy2O3 content at identical temperaturelevels. The measured thermal conductivity of La1�xDyxMgAl11O19 ceramics is located in the range of 2.52–2.89 W m�1 K�1 at 1200 �C. Thermal expansion coefficient of La0.8Dy0.2MgAl11O19 ceramic is slightlyhigher than that of undoped LaMgAl11O19 ceramic at identical temperature levels.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Lanthanum magnesium hexaaluminate (LnMgAl11O19, LHA)complex oxides with magnetoplumbite structure have attractedmuch attention as thermal barrier coatings (TBCs) materials,dielectric resonators, active elements of solid-state lasers, andcatalytic combustion supports or catalysts [1–7]. In the magneto-plumbite structure, one rare-earth oxide layer as a crystallographicmirror plane is followed by four spinel layers [1]. The rare-earthatom in the mirror plane located in an oxygen position suppressesthe diffusion processes and leads to crystallize in the habit plane oflayered structure [2].

Thermal barrier coatings produced by plasma-spraying (PS) orelectron-beam physical vapor deposition (EB-PVD) methods havebeen widely used to protect hot-section metallic components inadvanced gas-turbine and diesel engines [8,9]. Generally, lowthermal conductivity, high thermal expansion coefficient, highmelting point and sintering resistance at elevated temperaturesare needed as TBCs materials [10]. The current state-of-the-artthermal barrier coating material is 7–8 wt.% yttria stabilized zir-conia (7–8YSZ), which starts rapid degradation at operating tem-peratures above 1200 �C due to phase transitions and serioussintering phenomenon [8,10,11]. LHA has high operating temper-ature (>1300 �C [1]), good thermochemical stability (>1400 �C[12]), low thermal conductivity (1.2–2.6 W m�1 K�1 [12]), and

ll rights reserved.

1.).

high thermal expansion coefficient (9.5–10.7 � 10�6 K�1 [12]) asa potential TBC candidate. The results of water quenching testsindicated that thermal shock resistance of LnMgAl11O19 (Ln = La,Nd, Sm, Gd) is superior to that of 8YSZ [13]. LaLiAl11O18.5 mayform segmentation cracks during heat treatment leading to a con-siderable expansion tolerance [14]. Bansal and Zhu [15] synthe-sized LnMgAl11O19 (Ln = La, Gd, Sm) and Gd0.7Yb0.3MgAl11O19 bycitric acid sol–gel method and examined the effect of rare-earthoxide doping on thermal properties. Thermal conductivity ofGd0.7Yb0.3MgAl11O19 composition was lower than that of undopedGdMgAl11O19, however, thermal expansion coefficient was inde-pendent of the composition. In the comparison on ambient-tem-perature mechanical properties, magnetoplumbite oxides ofLaMnAl11O19, LaMgAl11O19 and LaZnAl11O19 exhibited a higherstrength (>300 MPa) and a higher fracture toughness(>3 MPa m1/2) than the pyrochlore oxides of Ln2Zr2O7 (Ln = La,Nd, Gd) [16]. In the development of the TBC materials, especiallyin the latest 10 years, there are many reports on doping with oneor multi-trivalent rare-earth elements at the A sites in A2Zr2O7

pyrochlore, such as (SmxGd1�x)2Zr2O7 [17], La2�xNdxZr2O7 [18],La1.7Gd0.3Zr2O7, La1.7Yb0.3Zr2O7, La1.7Gd0.15Yb0.15Zr2O7 [19], to im-prove their thermophysical properties.

In the present study, Dy3+ cation was introduced into the struc-ture of LaMgAl11O19 at La3+ site. La1�xDyxMgAl11O19 (x = 0, 0.1,0.2, 0.3) ceramics with a magnetoplumbite structure wereproduced by pressureless-sintering process at 1700 �C for 10 h inair. The influence of dysprosium oxide doping on thermophysicalproperties of LaMgAl11O19 ceramics was investigated.

10 20 30 40 50 60 70 80 90

(111

6)

(201

4)(220

)(201

1)(2

17)

(209

)

(101

1)

(206

)(205

)(0

010)

(203

)(1

14)

(112

)(008

)(110

)(1

07)

(105

)(006

)

(102

)(1

01)

Inte

nsity

(a.

u.)

2Theta (deg.)

x = 0

x = 0.2

x = 0.1

x = 0.3

Fig. 1. XRD patterns of La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) ceramics sintered at

3354 Y.-H. Wang et al. / Materials and Design 31 (2010) 3353–3357

2. Experimental

2.1. Materials preparation and characterization

In the present study, lanthanum oxide and dysprosium oxidepowders (Grirem Advanced Materials Co. Ltd., Beijing, China; pur-ity P99.9%), aluminum nitrate (Al(NO3)3�9H2O) and magnesiumnitrate (Mg(NO3)2�6H2O) (Tianjin Guangfu Fine Chemical ResearchInstitute Ltd., Analytical pure) were used as the reactants. La1�x-

DyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) powders were synthesized bychemical-coprecipitation and calcination method. La2O3 andDy2O3 powders were calcined at 900 �C for 2 h in air to removeabsorptive water and carbon dioxide before weighing. La2O3 andDy2O3 were dissolved in dilute hydrogen nitrate, while Al(-NO3)3�9H2O and Mg(NO3)2�6H2O were dissolved in de-ionizedwater. Above two solutions were mixed in appropriate mole ratiosof La1�xDyxMgAl11O19 (where x = 0, 0.1, 0.2, 0.3) under continuousstirring. The precursor solution was slowly added under stirringinto excessive ammonium hydrate solution with a pH value of 12to obtain gel-like precipitates. After that, these gels were washedwith de-ionized water several times until pH = 7, and were thenwashed twice with absolute alcohol. The remains were dried at80 �C for 24 h and calcined at 800 �C for 5 h in air for crystalliza-tion. The La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) ceramic powderswere preformed at 20 MPa for 2 min, cold isostatically pressed at280 MPa for 5 min, and then pressureless-sintered at 1700 �C for10 h in air to obtain densified samples for thermophysical proper-ties measurements.

Crystal structure of sintered La1�xDyxMgAl11O19 ceramics wasidentified by X-ray diffractometer (XRD, Rigaku D/Max 2200VPC,Japan) with Cu Ka radiation at a scan rate of 4 deg/min. The mor-phologies of La1�xDyxMgAl11O19 ceramics were characterized byscanning electron microscope (SEM, CamScan MX 2600FE, UK).The sintered specimens were carefully ground, polished and ther-mally etched at 1550 �C for 1 h in air for SEM observations. Thedensities of La1�xDyxMgAl11O19 ceramics were measured by theArchimedes method with an immersion medium of de-ionizedwater. The theoretical densities of all compositions were calculatedusing lattice parameters acquired from XRD results and relativemass of one unit cell.

2.2. Thermophysical properties measurements

Thermal diffusivity of La1�xDyxMgAl11O19 ceramics was mea-sured using the laser-flash diffusivity technique (Netzsch LFA427, Germany) from room temperature to 1200 �C in an argonatmosphere. The dimensions of the disc-shaped samples were12.7 mm in diameter and 2.0 mm in thickness. Prior to thermal dif-fusivity measurement, the surfaces of the specimens were coatedwith a thin layer of sprayed colloidal graphite. This coating wasdone to minimize the radiative transport of the thermal flashthrough the samples, and to prevent direct transmission of the la-ser beam through the translucent specimens at high temperatures.Appropriate corrections were made in the thermal diffusivity cal-culations to account for the presence of these layers. The thermaldiffusivity measurement of all specimens was carried out threetimes at each temperature. The specific heat capacities were calcu-lated from the chemical compositions of La1�xDyxMgAl11O19

ceramics with the Neumann–Kopp rule as a function of tempera-ture. The heat capacity data of the component oxides (La2O3,Dy2O3, MgO, Al2O3) were obtained from the literature [20]. Thethermal conductivity k was determined from the heat capacityCp, density q and thermal diffusivity k, and using the followingequation:

k ¼ Cp � q � k ð1Þ

As the sintered specimens were not fully dense, the measuredthermal conductivity data were corrected for the residual porosityu of the samples, using the equation [21],

kk0¼ 1� 4

3u ð2Þ

where k0 is the corrected thermal conductivity for fully densematerials.

The linear thermal expansion coefficients of sintered ceramicsusing the specimens with the dimensions of 2.5 mm � 3.5 mm �14.0 mm were determined by a high-temperature dilatometer(Netzsch DIL 402C, Germany) in an argon atmosphere. Specimenswere measured in the temperature range of 50–1200 �C at a heat-ing rate of 4 �C/min during heating, and were corrected by theknown thermal expansion of a certified standard alumina. Thethermal expansion coefficient is given by

aðT1�T2Þ ¼ðDL=L0ÞðT2Þ � ðDL=L0ÞðT1Þ

T2 � T1ð3Þ

where aðT1�T2Þ represents the average change of length for unitlength specimen between the range of T1 and T2.

3. Results and discussion

3.1. Characterization of La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3)ceramics

X-ray diffraction patterns of La1�xDyxMgAl11O19 ceramics sin-tered at 1700 �C for 10 h in air are shown in Fig. 1. All peaks inthe XRD patterns of La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) ceram-ics match well with the magnetoplumbite crystal structure (JCPDSNo. 77-1429). This indicates that Dy3+ cations successfully occupypartial sites of La3+ cations in the crystal structure and form substi-tution solid solutions. The theoretical densities were calculatedaccording to the XRD results. The bulk densities of La1�xDyxMgA-l11O19 ceramics were measured by Archimedes method with animmersion medium of de-ionized water. Table 1 shows the relativedensity of La1�xDyxMgAl11O19 ceramics sintered at 1700 �C for10 h. The relative densities of La1�xDyxMgAl11O19 ceramics are inthe range of 90.7–96.0%, and La0.8Dy0.2MgAl11O19 has the highestrelative density of 96.0%. Fig. 2 shows the microstructure of La1�x-

DyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) ceramics sintered at 1700 �C for10 h. From the SEM observations, the grains in La1�xDyxMgAl11O19

1700 �C for 10 h.

Y.-H. Wang et al. / Materials and Design 31 (2010) 3353–3357 3355

are inhomogeneous, and the platelets distribute randomly with asize of 1–20 lm.

3.2. Thermal conductivity of La1�xDyxMgAl11O19 ceramics

The calculated specific heat capacities of La1�xDyxMgAl11O19

ceramics based on Neumann–Kopp rule at different temperatureswere shown in Table 2. The thermal diffusivity of La1�xDyxMgA-l11O19 (x = 0, 0.1, 0.2, 0.3) ceramics as a function of temperature isshown in Fig. 3. The thermal diffusivity values in Fig. 3 are thearithmetic means of every three measurements of identical cera-mic materials. The error derived from the mean standard deviationfor three measurements of each specimen is less than 0.9%, and the

Table 1The relative density of La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) ceramics sintered at1700 �C for 10 h.

Ceramic materials Relative density (%)

LaMgAl11O19 90.7La0.9Dy0.1MgAl11O19 93.0La0.8Dy0.2MgAl11O19 96.0La0.7Dy0.3MgAl11O19 95.6

Fig. 2. Microstructure of La1�xDyxMgAl11O19 ceramics sintered at 1

Table 2Specific heat capacities of La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) bulk ceramics calculated

Ceramic bulk materials Specific heat capacities (J g�1 K�1)

25 �C 200 �C 400 �C

LaMgAl11O19 0.6757 0.9003 0.9837La0.9Dy0.1MgAl11O19 0.6741 0.8978 0.9809La0.8Dy0.2MgAl11O19 0.6726 0.8954 0.9781La0.7Dy0.3MgAl11O19 0.6710 0.8929 0.9753

error bars in Fig. 3 are smaller than the symbols. Clearly, the ther-mal diffusivity of La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) decreasesrapidly with increasing temperature from room temperature to800 �C, which suggests a dominant phonon conduction behaviorin most inorganic non-metallic materials [22]. The measured ther-mal diffusivity of La1�xDyxMgAl11O19 ceramics keeps almost un-changed above 800 �C due to the radiative contribution at hightemperatures [19]. Thermal diffusivity of La1�xDyxMgAl11O19

ceramics decreases with increasing Dy2O3 content at identical tem-perature levels. The decrease in thermal diffusivity at identicaltemperature levels is assigned to the lattice distortion due toDy3+ cations substitution for La3+ cations in the structure. Cationsubstitution causes lattice distortion, increases phonon scatteringand decreases phonon mean free path. On the other hand, the pho-non mean free path is proportional to the square of atomic weightdifference between the solute and host cations, according to thefollowing Eq. (4) [23]:

l�l¼ a3

4pm4 w4cDMM

� �2

ð4Þ

where a3 is the volume per atom, m is the transverse wave speed, xis the phonon frequency, c is the concentration per atom, M is the

700 �C for 10 h: (a) x = 0, (b) x = 0.1, (c) x = 0.2, and (d) x = 0.3.

with the Neumann–Kopp rule at different temperatures.

600 �C 800 �C 1000 �C 1200 �C

1.0273 1.0577 1.0826 1.10461.0243 1.0546 1.0794 1.10141.0213 1.0516 1.0763 1.09821.0184 1.0485 1.0731 1.0950

0 200 400 600 800 1000 12000.2

0.4

0.6

0.8

1.0

1.2

1.4

The

rmal

dif

fusi

vity

m

m2 s-1

Temprature oC

LaMgAl11

O19

La0.9

Dy0.1

MgAl11

O19

La0.8

Dy0.2

MgAl11

O19

La0.7

Dy0.3

MgAl11

O19

Fig. 3. Thermal diffusivity of La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) ceramics as afunction of temperature.

0 200 400 600 800 1000 1200

2

3

4

5

LaMgAl11

O19

La0.9

Dy0.1

MgAl11

O19

La0.8

Dy0.2

MgAl11

O19

La0.7

Dy0.3

MgAl11

O19

The

rmal

con

duct

ivity

W

m-1

K-1

Temperature oC

Fig. 4. Thermal conductivity of La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) ceramics as afunction of temperature.

0 200 400 600 800 1000 1200

0.0

0.2

0.4

0.6

0.8

1.0

LaMgAl11

O19

La0.8

Dy0.2

MgAl11

O19

dL/L

0 (%

)

Temperature oC

0 200 400 600 800 1000 12000

1

2

3

4

5

6

7

8

9

Temperature oC

TE

C

10-6

K-1 LaMgAl

11O

19

La0.8

Dy0.2

MgAl11

O19

(b)

(a)

Fig. 5. Thermal expansion analysis of LaMgAl11O19 and La0.8Dy0.2MgAl11O19

ceramics: (a) dilatometric curves; (b) thermal expansion coefficient curves.

3356 Y.-H. Wang et al. / Materials and Design 31 (2010) 3353–3357

average mass of the host atom, DM is the weight difference be-tween the solute and host cations. Because the atomic weights ofLa and Dy are 138.9 and 162.5, respectively, the effective phononscattering by Dy3+ is significantly higher than that of La3+, whichcontributes to the lower thermal conductivity.

Thermal conductivity of La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3)ceramics is plotted in Fig. 4 according to Eq. (1) and the thermaldiffusivity, specific heat capacity and density of different samples.The values in Fig. 4 are corrected to a 100% theoretical densityaccording to Eq. (2) and Table 1. The error bars are omitted as theyare smaller than the symbols. From Fig. 5, the thermal conductivityof La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) ceramics is located in therange of 2.52–2.89 W m�1 K�1 at 1200 �C, and decreases withincreasing Dy2O3 content.

3.3. Thermal expansion of La1�xDyxMgAl11O19 ceramics

The thermal expansion of sintered LaMgAl11O19 and La0.8-

Dy0.2MgAl11O19 ceramics as a function of temperature are pre-sented in Fig. 5a. Typical linear thermal expansion coefficientsare obtained in the temperature range of 50 to 1200 �C. The linearthermal expansion coefficients of LaMgAl11O19 and La0.8Dy0.2MgA-

l11O19 ceramics increase with increasing temperature, which is atypical characteristic of solid materials [24,25]. At identical tem-perature levels, thermal expansion coefficient of La0.8Dy0.2MgA-l11O19 is higher than that of undoped LaMgAl11O19. According toTable 1, the relative density of La0.8Dy0.2MgAl11O19 is higher thanthat of undoped LaMgAl11O19. The average linear thermal expan-sion coefficient of LaMgAl11O19 and La0.8Dy0.2MgAl11O19 ceramicscalculated by Eq. (3) are shown in Fig. 5b. The thermal expansioncoefficient of La0.8Dy0.2MgAl11O19 ceramic is 8.64 � 10�6 K�1 at1200 �C, which is higher than that of LaMgAl11O19 (8.49 �10�6 K�1, 1200 �C). Reducing the interatomic bonding force in thecrystal structure is beneficial for its dilation and increasing thermalexpansion coefficient [18]. As the bond energy of Dy–O is lowerthan that of La–O, the increase in thermal expansion coefficientof La0.8Dy0.2MgAl11O19 ceramic can be explained by the incorpora-tion of Dy3+ atoms at La3+ cation sites.

4. Conclusions

(1) La1�xDyxMgAl11O19 (x = 0, 0.1, 0.2, 0.3) ceramics sintered at1700 �C for 10 h in air exhibit a single phase of magneto-plumbite structure. The relative density of La1�xDyxM-gAl11O19 ceramics is in the range of 90.7–96.0%.

(2) The thermal diffusivity of La1�xDyxMgAl11O19 ceramicsdecreases gradually with increasing temperature. Thermalconductivity of La1�xDyxMgAl11O19 ceramics is located in

Y.-H. Wang et al. / Materials and Design 31 (2010) 3353–3357 3357

the range of 2.52–2.89 W m�1 K�1 at 1200 �C, and decreaseswith increasing Dy2O3 content.

(3) Thermal expansion coefficient of La1�xDyxMgAl11O19 ceram-ics increase with increasing temperature. At identical tem-perature levels, thermal expansion coefficient ofLa0.8Dy0.2MgAl11O19 is higher than that of undopedLaMgAl11O19.

Acknowledgement

The authors would like to thank financial support from the Na-tional Natural Science Foundation of China (NSFC-No. 50972030).

References

[1] Gadow R, Lischka M. Lanthanum hexaaluminate – novel thermal barriercoatings for gas turbine applications – materials and process development.Surf Coat Technol 2002;151–152:392–9.

[2] Friedrich C, Gadow R, Schirmer T. Lanthanum hexaaluminte – a new materialfor atmospheric plasma spraying of advanced thermal barrier coatings. J ThermSpray Technol 2001;10:592–8.

[3] Iyi N, Jnoue Z, Takekawa S, Kimura S. The crystal structure of lanthanumhexaaluminate. J Solid State Chem 1984;54:70–7.

[4] Bijmon PB, Mohanan P, Sebastian MT. Microwave dielectric properties ofLaMgAl11O19. Mater Res Bull 2002;37:2129–33.

[5] Park JG, Cormack AN. Defect energetics and nonstoichiometry in lanthanummagnesium hexaaluminate. J Solid State Chem 1997;130:199–212.

[6] Wang JW, Tian ZJ, Xu JG, Xu YP, Xu ZS, Lin LW. Preparation of Mn substitutedLa–hexaaluminate catalysts by using supercritical drying. Catal Today2003;83:213–22.

[7] Yin FX, Ji SF, Wu PY, Zhao FZ, Li CY. Preparation, characterization, and methanetotal oxidation of AAl12O19 and AMAl11O19 hexaaluminate catalysts preparedwith urea combustion method. J Mol Catal A 2008;294:27–36.

[8] Clarke DR, Levi CG. Materials design for the next generation thermal barriercoatings. Annu Rev Mater Res 2003;33:383–417.

[9] Padture NP, Gell M, Jordan EH. Thermal barrier coatings for gas-turbine engineapplications. Science 2002;296:280–4.

[10] Cao XQ, Vassen R, St}oever D. Ceramic material for thermal barrier coatings. JEur Ceram Soc 2004;24:1–10.

[11] Vourlias G, Pistofidis N, Psyllaki P, Pavlidou E, Stergioudis G, Chrissafis K.Plasma sprayed YSZ coatings: microstructure features and resistance tomolten metals. J Alloys Compd 2009;483:382–5.

[12] Schafer GW, Gadow G. Lanthane aluminate thermal barrier coating. Ceram EngSci Proc 1999;20:291–7.

[13] Zhang J, Zhong X, Cheng Y, Wang Y, Xu Z, Chen X, et al. Thermal-shockresistance of LnMgAl11O19 (Ln = La, Nd, Sm, Gd) with magnetoplumbitestructure. J Alloys Compd 2009;482:376–81.

[14] Pracht G, Vaßen R, St}over D. Lanthanum–lithium hexaaluminate – a newmaterial for thermal barrier coatings in magnetoplumbite structure – materialand process development. Ceram Eng Sci Proc 2006;27:87–9.

[15] Bansal NP, Zhu DM. Thermal properties of oxides with magnetoplumbitestructure for advanced thermal barrier coatings. Surf Coat Technol2008;202:2698–703.

[16] Choi SR, Bansal NP, Zhu DM. Mechanical and thermal properties of advancedoxide materials for higher-temperature coatings applications. Ceram Eng SciProc 2001;10:592–8.

[17] Liu ZG, Ouyang JH, Zhou Y. Structural evolution and thermophysical propertiesof (SmxGd1�x)2Zr2O7 (0 6 x 6 1.0) ceramics. J Alloys Compd 2009;472:311–6.

[18] Wang J, Bai SX, Zhang H, Zhang CR. The structure, thermal expansioncoefficient and sintering behavior of Nd3+-doped La2Zr2O7 for thermalbarrier coatings. J Alloys Compd 2009;476:89–97.

[19] Bansal NP, Zhu DM. Effects of doping on thermal conductivity of pyrochloreoxides for advanced thermal barrier coatings. Mater Sci Eng A2007;459:192–5.

[20] Kubaschewsji O, Alcock CB, Spencer PJ. Materials thermochemistry. 6thed. Pergamon Press; 1993. p. 257–323.

[21] Wu J, Wei XZ, Padture NP, Klemens PG, Gell M, Garcia E, et al. Low-thermal-conductivity rare-earth zirconates for potential thermal-barrier-coatingapplications. J Am Ceram Soc 2002;85:3031–5.

[22] Remy M, Jean-Claude L, Alban A, Berangere L, Martine P, Odile L, et al. Thermaldiffusivity and conductivity of Zr1�xYxO2�x/2(x = 0, 0.084 and 0.179) singlecrystals. J Eur Ceram Soc 2004;24:3081–9.

[23] Zhou HM, Yi DQ, Yu ZM, Xiao LR. Preparation and thermophysical properties ofCeO2 doped La2Zr2O7 ceramic for thermal barrier coatings. J Alloys Compd2007;438:217–21.

[24] Liu ZG, Ouyang JH, Zhou Y, Xia XL. Phase stability and thermal expansionproperty of ZrO2–NdO1.5–AlO1.5 ceramics from 50 to 1550 �C. Mater Des2009;30:1845–9.

[25] Liu ZG, Ouyang JH, Zhou Y, Xia XL. Effect of Ti substitution for Zr on thethermal expansion property of fluorite-type Gd2Zr2O7. Mater Des2009;30:3784–8.